AU2018444217A1

AU2018444217A1 - Production method for briquette

Info

Publication number: AU2018444217A1
Application number: AU2018444217A
Authority: AU
Inventors: Daisuke Ariyoshi; Akira FUJIYOSHI; Katsushi Kosuge; Eiichiroh MORI; Yusuke URATA; Kazuma YASUDA
Original assignee: Nippon Steel Engineering Co Ltd
Current assignee: Nippon Steel Engineering Co Ltd
Priority date: 2018-10-03
Filing date: 2018-10-03
Publication date: 2021-05-20
Anticipated expiration: 2038-10-03
Also published as: WO2020070838A1; CN112805356B; CN112805356A; AU2018444217B2

Abstract

Provided is a production method that is for a briquette and that comprises a step for obtaining a briquette having a water content of 5 wt% or less by molding a molding raw material containing a powder carbonized coal and a binder and drying the same at 60-100°C. The binder contains an aqueous solution of a polyvinyl alcohol having a saponification degree of more than 99.3 mol% and a polymerization degree of 1700 or more. The powder carbonized coal is a pulverized coal obtained by drying and carbonizing a coal including brown coal and/or subbituminous coal.

Description

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DESCRIPTION Title of Invention PRODUCTION METHOD FOR BRIQUETTE Technical Field

[0001] The present disclosure relates to a production method for a briquette. Background Art

[0002] Fine coal in powder form is generated in a coal production process. It is difficult to handle fine coal, and fine coal can cause generation of powdery dust. Accordingly, effective utilization of fine coal by agglomerating fine coal into briquettes is being studied. For example, Patent Document 1 proposes a technique of adding starch as a binder to coal in powder form, mixing the mixture, and coating a surface of an agglomerated product obtained by agglomerating with a heavy oil component such as heavy oil or tar. Patent Document 2 proposes a technique of adding tar or tar slag to fine coal and then agglomerating. Citation List Patent Literature

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 2003-64377

[Patent Document 2] Japanese Unexamined Patent Publication No. H9-3458 Summary of Invention Technical Problem

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[0004] Reforming techniques including drying, carbonization, and the like are being studied in order to effectively utilize low-grade coal such as lignite and subbituminous coal. Fine coal is generated during such a reforming process. It is desirable that the generated fine coal be transported as agglomerated briquettes rather than in powder form from the viewpoint of improving safety and preventing liquefaction. Briquettes are required to have high strength during transportation so that they are not easily broken by vibration, impact, and the like. In addition, because briquettes are exposed to rain and wind during marine transport and storage of coal, briquettes are required to maintain high strength without collapsing even when they are wet with water.

[0005] It is more difficult to agglomerate fine coal of carbonized coal as compared to raw coal, and therefore a binder is required to produce briquettes. In a case where a heavy oil component such as tar is used as a binder, heating is required when kneading with fine coal. However, heating is not preferable from the viewpoint of safety because fine coal generated during carbonization easily ignites spontaneously. Furthermore, a heating facility is required and it is difficult to uniformly perform heating when kneading a large amount, and therefore there is a concern of non-uniform kneading and variation in the strength of briquettes.

[0006] In addition, in a case where starch is used as a binder and a surface is coated with an oil-based binder, and when a briquette cracks and the inside is exposed in this case, there is a concern of a decrease in strength when the briquette is wet with water because the starch is water-soluble. Under these circumstances, it is required to establish a

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technique for producing a briquette having high safety and excellent water resistance.

[0007] Accordingly, in one aspect, an object of the present invention is to provide a production method for a briquette that has excellent safety and can maintain high strength even when it is wet with water. Solution to Problem

[0008] In one aspect, the present invention provides a production method for a briquette, the method including a step of agglomerating an agglomerating raw material containing carbonized coal in powder form and a binder and drying at 60°C to 100°C to obtain the briquette having a moisture content of 5% by weight or less, in which the binder contains an aqueous solution of a polyvinyl alcohol having a degree of saponification of more than 99.3 mol% and a degree of polymerization of 1,700 or more, and the carbonized coal in powder form is fine coal obtained by drying and carbonizing coal containing at least one of lignite and subbituminous coal.

[0009] In this production method, the binder containing an aqueous solution of a polyvinyl alcohol having a degree of saponification of more than 99.3 mol% is used. Since an aqueous solution is used as the binder as described above, excellent safety is exhibited. In addition, in a case where drying is performed, in a polyvinyl alcohol having a high degree of saponification, hydroxyl groups in each of molecules are bonded to each other by hydrogen bonds, and thereby excellent water resistance is exhibited. That is, molecules of the polyvinyl alcohol contained in the binder in the briquette are strongly bonded to each

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other, and thereby high strength can be maintained even when the briquette is wet with water.

[0010] A degree of polymerization of the polyvinyl alcohol is preferably 2,500 or more. Accordingly, it is possible to further improve the strength of the briquette particularly in a case where the briquette is dried.

[0011] In the above-described step, an agglomerated product of the agglomerating raw material is dried to obtain the briquette having a moisture content of 5% by weight or less. By reducing a moisture content of the agglomerated product as described above, formation of hydrogen bonds is promoted, and the strength of the briquette when the briquette is wet with water can be increased.

[0012] A content of the polyvinyl alcohol in the aqueous solution of the polyvinyl alcohol is preferably 1% to 10% by mass. Then, dispersibility between the carbonized coal in powder form and the binder becomes favorable, and uniformity of the agglomerating raw material can be improved. Accordingly, variation in the strength of the briquette can be reduced.

[0013] A content of the polyvinyl alcohol with respect to 100 parts by weight of the carbonized coal is preferably 1 part by weight or more. Then, the strength of the briquette can be further increased.

[0014] The binder may contain a-starch together with the polyvinyl alcohol. Manufacturing costs can be reduced in this case because a-starch is inexpensive. In addition, in a case of using a-starch, the strength of the briquette in a case of drying the briquette can be sufficiently increased. Accordingly, a-starch is useful in usage

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applications in which strength in a case of drying is more important than water resistance.

[0015] A crushing strength of the briquette, which is obtained by the above-described production method, after being immersed in water at 20°C for 24 hours is preferably 50 N or more. Accordingly, it is possible to sufficiently inhibit collapse due to exposure to rain and wind during transportation and storage of coal.

[0016] It is preferable that neither calcium oxide nor magnesium oxide be added to the agglomerating raw material. Accordingly, a heating value can be sufficiently increased when the briquette is used as an agglomerated fuel.

[0017] A crushing strength of the briquette after being immersed in water at 20°C for 24 hours is preferably 50 N or more. With this crushing strength, it is possible to sufficiently inhibit collapse due to exposure to rain and wind during transportation and storage of coal. Accordingly, marine transport and storage of coal can be safely performed, and thereby the briquette obtained by the above-described production method can be suitably used as an agglomerated fuel. Advantageous Effects of Invention

[0018] In one aspect, the present invention can provide a production method for a briquette that has excellent safety and can maintain high strength even when it is wet with water. Brief Description of Drawings

[0019] FIG. 1 is a schematic view of a measuring device used for measuring a crushing strength of a briquette.

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FIG. 2 is a semi-logarithmic graph showing a relationship between an immersion time and a crushing strength of briquettes of Examples 2 and 3 and Comparative Examples 2 and 3. FIG. 3 is a semi-logarithmic graph showing a relationship between an immersion time and a crushing strength of briquettes of Reference Examples 4 to 6. FIG. 4 is a graph which plots data of the briquettes of Reference Examples 4 to 6 before being immersed (after being dried) and after being immersed for 24 hours (1,440 minutes) in water with a crushing strength as a vertical axis and a degree of polymerization of a polyvinyl alcohol as a horizontal axis. FIG. 5 is a semi-logarithmic graph showing a relationship between an immersion time and a crushing strength of briquettes of Reference Examples 6 to 10. FIG. 6 is a semi-logarithmic graph showing a relationship between an immersion time and a crushing strength of briquettes of Reference Examples 11 to 13. FIG. 7 is a graph which plots data of the briquettes of Reference Example 8 and Reference Examples 11 to 13 before being immersed (after being dried) and after being immersed for 24 hours (1,440 minutes) in water with a crushing strength as a vertical axis and a blending ratio of a-starch as a horizontal axis. Description of Embodiments

[0020] Hereinafter, embodiments of the present invention will be described with reference to drawings in some cases. However, the following embodiments are exemplifications for describing the present

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invention and are not intended to limit the present invention to the following contents.

[0021] A production method for a briquette of the present embodiment includes a step of agglomerating an agglomerating raw material containing carbonized coal in powder from and a binder and drying to obtain the briquette. The carbonized coal in powder from is fine coal obtained by drying and carbonizing coal containing at least one of lignite and subbituminous coal. Accordingly, it is possible to effectively utilize lignite and subbituminous coal which are low-grade coals among coals. A particle size of the carbonized coal is not particularly limited, and the carbonized coal may be fine coal obtained by sieving carbonized coal with, for example, a sieve of 1 to 10 mm. A proportion of sieved carbonized coal obtained by sieving coal with a 1 mm sieve in the entire carbonized coal may be 80% by weight or more from the viewpoint of improving formability.

[0022] The binder contains an aqueous solution of a polyvinyl alcohol (PVA) having a degree of saponification of more than 99.3 mol% and a degree of polymerization of 1,700 or more. Fine coal obtained by drying and carbonizing low-grade coal such as lignite and subbituminous coal has more pores than coke powder produced from high-grade coal. Accordingly, an agglomerated product of such fine coal is likely to have a low density and a low strength. However, in the present embodiment, it is possible to increase strength by using the above-mentioned binder.

[0023] A degree of saponification of polyvinyl alcohol (PVA) represents a percentage of units that are actually saponified to vinyl

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alcohol units among units that can be converted to vinyl alcohol units by saponification. The degree of saponification can be measured by a neutralization titration method according to JIS K 6726-1994. Specifically, a phenolphthalein solution is added to a polyvinyl alcohol, and sodium hydroxide is added dropwise until the solution becomes pale pink. Residues (residual acetic acid groups) are obtained from an amount of dropwise addition to calculate a degree of saponification.

[0024] That is, a degree of saponification is calculated from an expression: n/(m + n) x 100 in a polyvinyl alcohol having a molecular structure as shown in Formula (1). A partially saponified polyvinyl alcohol has a molecular structure as shown in Formula (1), whereas a fully saponified polyvinyl alcohol has a molecular structure as shown in Formula (2) in which acetic acid groups are almost entirely substituted by hydroxyl groups.

[0025] [Chem. 1]

CH 2 -CH CH 2-CH (1) OH O

C=o

OH 3

[0026] [Chem. 2]

CH2-C\ CH2-CH (2) O nOH "

[0027] In a case where drying is performed, in a polyvinyl alcohol having a degree of saponification of more than 99.3 mol%, hydroxyl groups of each of molecules are strongly bonded to each other by

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hydrogen bonds. Once such bonds are formed, the bonds do not dissociate easily even when coming into contact with water again. Accordingly, when agglomerating and drying are performed while using a binder containing an aqueous solution of a polyvinyl alcohol having a degree of saponification of more than 99.3 mol% to obtain the briquette, this briquette has excellent water resistance. A degree of saponification of the polyvinyl alcohol is preferably 99.5 mol% or more from the viewpoint of further increasing a strength of the briquette when it is dried and when it is wet with water.

[0028] Commercially available products can be used for a polyvinyl alcohol. A degree of polymerization of the polyvinyl alcohol is 1,700 or more, is preferably 2,500 or more, and is more preferably 3,300 or more, from the viewpoint of improving the strength of the briquette particularly when it is dried. The degree of polymerization of a polyvinyl alcohol can be measured by a solution viscosity measurement method according to JIS K 6726-1994.

[0029] A content of polyvinyl alcohol in the aqueous solution of a polyvinyl alcohol is preferably 1% to 10% by weight and is more preferably 2% to 10% by weight. Accordingly, it becomes easier to knead with the carbonized coal in powder from, and it is possible to make dispersibility favorable. Therefore, uniformity of agglomerating raw materials is improved, and variation in the strength of briquettes can be reduced. A viscosity (20°C) of the aqueous solution of a polyvinyl alcohol may be, for example, 20 to 500 mPa-s.

[0030] Since the binder contains the aqueous solution, it has excellent safety as compared with a binder formed of only combustible materials.

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In addition, because carbonized coal and the binder can be kneaded even at room temperature without heating, even carbonized coal having spontaneous ignition properties can be kneaded sufficiently and safely. However, kneading by heating is not excluded.

[0031] The agglomerating raw material can be prepared by blending the carbonized coal in powder from and the binder containing the aqueous solution of a polyvinyl alcohol and kneading the mixture. Kneading may also be performed with addition of water depending on a viscosity of the aqueous solution of a polyvinyl alcohol or a content of polyvinyl alcohol in the aqueous solution. A blending ratio of the aqueous solution of a polyvinyl alcohol with respect to 100 parts by mass of the carbonized coal in powder from may be, for example, 5 to 50 parts by weight, or may be, for example, 5 to 30 parts by weight, from the viewpoint of sufficiently increasing both formability and kneading properties to a high level.

[0032] A content of polyvinyl alcohol in the agglomerating raw material is preferably 0.5% by weight or more and is more preferably 1.5% by weight or more from the viewpoint of sufficiently increasing the strength of briquettes. Meanwhile, a content of polyvinyl alcohol in the agglomerating raw material is preferably 10% by weight or less from the viewpoint of reducing manufacturing costs of briquettes. A moisture content in the agglomerating raw material is preferably 20% to 40% by weight from the viewpoint of sufficiently increasing both formability and kneading properties to a high level.

[0033] The binder may contain components other than a polyvinyl alcohol and water. Such components may be water-soluble

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components. As a water-soluble component, a-starch is preferable from the viewpoint of manufacturing costs. Manufacturing costs of the briquettes can be reduced by substituting some of polyvinyl alcohols by a-starch because a-starch is generally cheaper than polyvinyl alcohols. In addition, in a case of using a-starch, the strength of the briquette in a case of drying it can be sufficiently increased. In the agglomerating raw material, a blending ratio of a-starch with respect to 100 parts by weight of carbonized coal is preferably 1 to 9 parts by weight from the viewpoint of sufficiently increasing strength at the time of drying while maintaining water resistance.

[0034] It is preferable that neither calcium oxide nor magnesium oxide be added to the agglomerating raw material from the viewpoint of sufficiently increasing a heating value when the briquette is used as an agglomerated fuel.

[0035] Examples of apparatuses for agglomerating the agglomerating raw material include general apparatuses such as a double-roll agglomerating machine and a uniaxial press agglomerating machine. A shape of an agglomerated product to be obtained by agglomerating the agglomerating raw material is not particularly limited, and it may be, for example, a Maschec type, a spherical shape, a cylindrical shape, or a prismatic shape. A density of the briquette may be, for example, 1.0 to 2.0 g/ml. An agglomerating pressure is, for example, 1 to 10 ton/cm in linear pressure, and it is, for example, 40 to 390 MPa in contact pressure.

[0036] Subsequently, the obtained agglomerated product is dried using, for example, an electric furnace, a dryer, or the like to reduce a moisture

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content thereof. The briquette is obtained by drying the agglomerated product. The drying may be performed, for example, in air or an inert gas atmosphere at 60°C to 100°C. A drying time may be, for example, 1 to 20 hours. By drying at a relatively low temperature of 60°C to 100°C, it is possible to produce the briquette that can maintain high strength even when it is wet with water. The drying may be performed in an exhaust gas from a combustion furnace. Such drying reduces a moisture content of the briquette preferably to 5% by weight or less. With such a moisture content, hydrogen bonding between polyvinyl alcohol molecules (between hydroxyl groups) is sufficiently promoted, and thereby the strength of the briquette can be further increased. A moisture content of the briquette can be measured by a heating and drying method (method of measuring a weight before and after heating and drying) using a moisture measuring machine.

[0037] The briquette contains carbonized coal, and the binder containing a polyvinyl alcohol having a degree of saponification of more than 99.3 mol% and a degree of polymerization of 1,700 or more. In the briquette, a content of polyvinyl alcohol with respect to 100 parts by weight of carbonized coal is preferably 1 part by weight or more and is more preferably 2 parts by weight or more from the viewpoint that then, water resistance of such a briquette is excellent, and the strength thereof can be sufficiently increased. In the briquette, a content of polyvinyl alcohol with respect to 100 parts by weight of carbonized coal is, for example, 10 parts by weight or less from the viewpoint of manufacturing costs. A moisture content of the briquette is 5% by weight or less and is preferably 4% by weight or less from the

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viewpoint of improving strength. In a case where the binder contains a polyvinyl alcohol and a-starch, in the briquette, a content of a-starch with respect to 100 parts by weight of carbonized coal is preferably 1 to 9 parts by weight, and a total content of polyvinyl alcohol and a-starch is preferably 2 to 10 parts by weight.

[0038] The strength of the briquette can be quantitatively determined as a crushing strength measured using a measuring device 10 shown in FIG. 1. A cylindrical (<p 15 mm x height 15 mm) briquette 16 is prepared as a sample. The briquette 16 is disposed on a support plate 17 disposed on a bottom plate of a stand 18 such that a circumferential surface of the briquette 16 which is a measurement target and an upper surface of the support plate 17 come into contact with each other. Then, a movable plate 14, which is attached to the stand 18 in an up-and-down movable manner, is lowered to sandwich the briquette 16 between the movable plate 14 and the support plate 17. Then, the movable plate 14 is operated to apply a load to the briquette 16 in a radial direction of the briquette 16. Finally, crushing strength is obtained from a load at which the briquette 16 fractures.

[0039] A crushing strength of the briquette is preferably 100 N or more and is more preferably 150 N or more when the briquette is dried (moisture content: 2 to 4% by weight). In addition, a crushing strength of the briquette after being immersed in water at 20°C for 24 hours is preferably 40 N or more and is more preferably 50 N or more. As described above, the briquette of the present embodiment can maintain high strength not only when it is dried but also when it is wet with water.

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[0040] Hereinbefore, the embodiments of the present invention have been described, but the present invention is not limited to the above-described embodiments. Examples

[0041] The contents of the present invention will be described in more detail with reference to examples, reference examples, and comparative examples, but the present invention is not limited to the following examples.

[0042] [Examination of binder type] (Example 1 and Comparative Example 1) <Preparation of agglomerating raw materials> The following 12 types of binders were prepared. (1) An aqueous solution of polyvinyl alcohol (degree of polymerization: 1,700, degree of saponification: 99.7 mol%) (content of polyvinyl alcohol: 10% by weight) (2) a-Starch (derived from corn) (3) a-Starch (derived from tapioca) (4) Straight asphalt (5) Soft pitch (SOP) (6) Bitumen A (7) Bitumen B (8) Vinyl acetate emulsion (9) Molasses A (calcium hydroxide not added) (10) Molasses B (calcium hydroxide added) (11) Pulp waste liquid (12) Alkaline aqueous solution of fumic acid

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(13) Bentonite

[0043] Carbonized coal obtained by carbonization was sieved with a 1 mm sieve, and the obtained sieved carbonized coal and the above-mentioned binders (1) to (13) were respectively kneaded to obtain agglomerating raw materials. The binders (1) and (8) to (13) could be kneaded at room temperature to prepare agglomerating raw materials. On the other hand, the binders (4) to (7) had high viscosities, it was difficult to knead them at room temperature (20°C). Accordingly, the binders (4) to (7) were kneaded with carbonized coal while being heated to 120°C to 130°C to prepare agglomerating raw materials.

[0044] <Production of briquettes and evaluation of formability> The prepared agglomerating raw materials were agglomerated at an agglomerating pressure of 283 MPa using a uniaxial pressure agglomerating machine to prepare briquettes. For each of the binders, a blending amount of the binder required to make a crushing strength of a briquette 50 N or more was investigated. Then, formability of each of the binders was evaluated according to the following criteria. That is, evaluation was as follows: "A" was a case in which a content of the binder with respect to the entire briquette was 10% by weight or less, "B" was a case in which a content of the binder was more than 10% by weight and equal to or less than 40% by weight, and "C" was a case in which agglomerating could not be performed even when a blending amount of the binder was 40% by weight, or a case in which a crushing strength did not reach 50 N. The evaluation results are as shown in Table 1.

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[0045] <Evaluation of water resistance of briquettes> Water resistance was evaluated for the cases with "A" or "B" as a result of formability evaluation by the following procedure. The briquettes were immersed in water for 1,440 minutes. Thereafter, the briquettes were taken out from the water, and a briquette that maintained a shape before immersion was evaluated as "A," and a briquette that could not maintain a shape before immersion was evaluated as "B." The evaluation results are as shown in Table 1.

[0046] [Table 1] Type of Whether heating is Formability Water binder required resistance Example 1 (1) Not required A A Comparative Example 1-1 (2) Not required | A | B Comparative Example 1-2 (3) Not required | A B Comparative Example 1-3 (4) Required | B A Comparative Example 1-4 (5) Required | B A Comparative Example 1-5 (6) Required C Comparative Example 1-6 (7) Required C Comparative Example 1-7 (8) Not required C Comparative Example 1-8 (9) Not required C Comparative Example 1-9 (10) Not required C Comparative Example 1-10 (11) Not required C Comparative Example 1-11 (12) Not required C Comparative Example 1-12 (13) Not required C

[0047] As shown in Table 1, as compared to those of Comparative Examples 1-3 to 1-12 in which the binders (4) to (13) were used, a briquette having excellent formability was obtained in Example 1 in which a polyvinyl alcohol was used as the binder. The briquette of Example 1 also had excellent water resistance. Although Comparative Examples 1-1 and 1-2 in which the binders (2) and (3) were used were excellent in formability, they collapsed when being immersed in water and could not maintain their original shapes.

[0048] [Influence of degree of saponification]

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(Example 2) An aqueous solution (aqueous binder solution) containing a polyvinyl alcohol (degree of saponification: > 99.85 mol%, degree of polymerization: 1,700) at a concentration of 10% by weight, water, and the carbonized coal used in Example 1 were mixed to obtain a mixture. A blending ratio based on the weight in this case was 30 parts by weight for the aqueous binder solution and 10 parts by weight for water with respect to 100 parts by mass of the carbonized coal. The mixture was agglomerated using a uniaxial pressure agglomerating machine (agglomerating pressure: 283 MPa) to prepare a plurality of briquettes (before drying). A moisture content of the briquette was 27.6% by weight, and a crushing strength (mean value of n = 2) thereof was 66 N. The crushing strength was measured using a measuring device shown in FIG. 1.

[0049] The produced briquettes were dried in air under conditions of 80°C for 15 hours. A moisture content and a crushing strength of the briquettes after drying are as shown in Table 2. Moisture contents of the briquettes before and after drying were measured by a heating and drying method using a commercially available moisture measuring machine.

[0050] A plurality of briquettes after drying were immersed in water at about 20°C for a predetermined time. After the elapse of the predetermined immersion time shown in Table 2, the briquettes were taken out from water, moisture contents were measured, and crushing strengths were measured (where a moisture content was not measured

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for some briquettes). Table 2 shows measurement results of an immersion time, a moisture content, and a crushing strength.

[0051] The briquettes immersed in water for 1,440 minutes were dried in air at 80°C for 15 hours. After this re-drying, a moisture content of the briquette was measured, and crushing strengths were measured. The results of the moisture content and the crushing strength are shown in Table 2.

[0052] [Table 2] Immersion time Moisture content Crushing strength (N) (minute) (% by weight) 11 2 Average Before drying 27.6 59 73 66.0 After drying - 180 164 172.0 After immersion 1 - 105 150 127.5 After immersion 30 8.3 148 108 128.0 After immersion 1440 18.2 91 101 96.0 After re-drying 3.6 100 103 101.5

[0053] As shown in Table 2, the briquettes of Example 2 were able to maintain a crushing strength of 90 N or more even after the lapse of 24 hours.

[0054] (Example 3) Briquettes were produced in the same manner as in Example 2 except that a polyvinyl alcohol (degree of saponification: > 99.3 mol%, degree of polymerization: 1,700) was used instead of the polyvinyl alcohol used in Example 2, and then measurements were performed. The results are shown in Table 3.

[0055] [Table 3] Immersion time Moisture content Crushing strength (N) (minute) (% by weight) 11 2 Average Before drying 28.7 30 35 32.5 After drying 3.6 114 119 116.5 After immersion 1 5.9 105 102 103.5 After immersion 30 7.8 118 111 114.5 After immersion 1440 18.1 74 73 73.5 After re-drying 3.1 94 98 96.0

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[0056] As shown in Table 3, the briquettes of Example 3 were able to maintain a crushing strength of 70 N or more even after the lapse of 24 hours. Example 2 in which a degree of saponification was high had higher crushing strength and excellent water resistance as compared to Example 3.

[0057] (Comparative Example 2) Briquettes were produced in the same manner as in Example 2 except that a polyvinyl alcohol (degree of saponification: 94.5 to 95.5 mol%, degree of polymerization: 1,700) was used instead of the polyvinyl alcohol used in Example 2, and then measurements were performed. The results are shown in Table 4.

[0058] [Table 4] Immersion time Moisture content Crushing strength (N) (minute) (% by weight) 1 1 2 Average Before drying 27.0 3 3 3.0 After drying - 16 14 15.0 After immersion 1 29.6 8 7 7.5 After immersion 30 41.4 2 3 2.5 After immersion 1440 - |- -

[0059] As shown in Table 4, the briquette of Comparative Example 2 had a significantly lower crushing strength after drying as compared to those of Examples 2 and 3. Furthermore, when the briquettes were immersed in water, the briquettes gradually collapsed, and therefore measurement after 30 minutes for an immersion time could not be performed.

[0060] (Comparative Example 3) Briquettes were produced in the same manner as in Example 2 except that a polyvinyl alcohol (degree of saponification: 87 to 89 mol%, degree of polymerization: 1,700) was used instead of the

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polyvinyl alcohol used in Example 2, and then measurements were performed. The results are shown in Table 5.

[0061] [Table 5] Immersion time Moisture content Crushing strength (N) (minute) (% by weight) 1 1 2 1 Average Before drying 26.3 | 2 |3 | 2.5 After drying 4.4 12 13 12.5 After immersion 1 35.4 | 4 |2_ | 3.0 After immersion 30 - - -

[0062] As shown in Table 5, the briquettes of Comparative Example 3 had a lower crushing strength after drying even than that of Comparative Example 2. Furthermore, when the briquettes of Comparative Example 2 were immersed in water, the briquettes gradually collapsed, and therefore measurements after 1 minute for an immersion time could not be performed.

[0063] FIG. 2 is a semi-logarithmic graph showing a relationship between an immersion time and a crushing strength of the briquettes of Examples 2 and 3 and Comparative Examples 2 and 3. For briquettes that were collapsed after being immersed in water, crushing strengths were set to 0 and plotted in a graph.

[0064] [Influence of degree of polymerization] (Reference Example 4) Briquettes were produced in the same manner as in Example 2 except that a polyvinyl alcohol (degree of saponification: > 99 mol%, degree of polymerization: 2,500) was used instead of the polyvinyl alcohol used in Example 2, and then measurements were performed. The results are shown in Table 6.

[0065] [Table 6] Degree of Immersion time | Moisture content Crushing strength(N)

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polymerization: (minute) (% by weight) 1 2 Average 2500 Before drying 26.2 86 82 84.0 After drying 3.1 121 146 133.5 After immersion 1 4.9 139 162 150.5 After immersion 30 2.4 173 173 173.0 After immersion 1440 18.2 117 136 126.5 After re-drying 3.0 96 102 99.0

[0066] As shown in Table 6, the briquettes of Reference Example 4 were able to maintain a crushing strength of 100 N or more even after the lapse of 24 hours for an immersion time.

[0067] (Reference Example 5) Briquettes were produced in the same manner as in Example 2 except that a polyvinyl alcohol (degree of saponification: > 99 mol%, degree of polymerization: 3,300) was used instead of the polyvinyl alcohol used in Example 2, and then measurements were performed. The results are shown in Table 7.

[0068] [Table 7] Degree of Immersion time Moisture content Crushing strength (N) polymerization: (minute) (% by weight) 1 2 Average Before drying 27.5 110 116 113.0 After dying 3.3 183 174 178.5 After immersion 1 4.9 204 209 206.5 After immersion 30 7.4 213 230 221.5 After immersion 1440 17.4 138 150 144.0 After re-drying 2.8 126 140 133.0

[0069] As shown in Table 7, the briquettes of Reference Example 5 were able to maintain a crushing strength of 100 N or more even after the lapse of 24 hours for an immersion time. Reference Example 5, in which a degree of polymerization of a polyvinyl alcohol was high, showed a higher crushing strength both before and after immersion in water, as compared with Reference Example 4.

[0070] (Reference Example 6)

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Briquettes were produced in the same manner as in Example 2 except that a polyvinyl alcohol (degree of saponification: > 99 mol%, degree of polymerization: 4,000) was used instead of the polyvinyl alcohol used in Example 2, and then measurements were performed. The results are shown in Table 8.

[0071] [Table 8] Degree of Immersion time Moisture content Crushing strength (N) polymerization: (minute) (% by weight) 1 2 Average 4000 _ _ _ __ _ _ _ 1 2 Before drying| 27.9 154 149 | 151.5 After drying 3.7 336 307 321.5 After immersion 1 5.2 289 307 298.0 After immersion 30 9.3 185 196 190.5 After immersion 1440 22.4 185 176 180.5 After re-drying 3.5 282 291 286.5

[0072] As shown in Table 8, the briquettes of Reference Example 6 were able to maintain a crushing strength of 100 N or more even after the lapse of 24 hours. The briquettes of Reference Example 6 in which a degree of polymerization of a polyvinyl alcohol was high had a particularly high crushing strength before immersion (before drying and after drying) and after re-drying, as compared with Reference Examples 4 and 5.

[0073] FIG. 3 is a semi-logarithmic graph showing a relationship between an immersion time and a crushing strength of the briquettes of Reference Examples 4 to 6. FIG. 4 is a graph which plots data of the briquettes of Reference Examples 4 to 6 before being immersed (after being dried) and after being immersed for 24 hours (1,440 minutes) in water with a crushing strength as a vertical axis and a degree of polymerization of a polyvinyl alcohol as a horizontal axis. As shown in FIGS. 3 and 4, as a degree of polymerization of a polyvinyl alcohol

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increases, a crushing strength and water resistance before immersion in water improve. Furthermore, crushing strengths of the briquettes after drying are significantly improved as a degree of polymerization of a polyvinyl alcohol increases.

[0074] [Influence of content of polyvinyl alcohol] (Reference Example 7) An aqueous binder solution used in Reference Example 6 and containing a polyvinyl alcohol (degree of saponification: > 99 mol%, degree of polymerization: 4,000) at a concentration of 10% by weight, water, and the carbonized coal used in Example 1 were mixed to prepare a mixture. A blending ratio based on the weight in this case was 3 parts by weight for the aqueous binder solution and 34.3 parts by weight for water with respect to 100 parts by mass of the carbonized coal. Briquette were produced using this mixture in the same manner as in Example 2, and then measurements were performed. The results are shown in Table 9.

[0075] [Table 9] Blending ratio of Immersion time Moisture content Crushing strength (N)

0.3partsbyweight (minute) (% by weight) 1 2 Average Before drying 27.5 13 | 14 13.5 After drying 3.9 11 11 11.0 After immersion 1 18.5 14 12 13.0 After immersion 30 22.4 13 11 12.0 After immersion 1440 36.5 9 10 9.5 After re-drying 3.9 6 7 6.5

[0076] (Reference Example 8) Briquettes were produced in the same manner as in Reference Example 7 except that a mixture was prepared with 10 parts by weight of the aqueous binder solution and 28 parts by weight of water with

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respect to 100 parts by weight of carbonized coal for a blending ratio of the aqueous binder solution, water, and carbonized coal based on the weight, and then measurements were performed. The results are shown in Table 10.

[0077] [Table 10] Blending ratio of Immersion time Moisture content Crushing strength (N)

1partbyweight (minute) (% by weight) 1 2 Average Before drying 27.5 67 71 69.0 After drying 4.2 75 80 77.5 After immersion 1 6.9 74 75 74.5 After immersion 30 10.6 65 70 67.5 After immersion 1440 26.1 56 57 56.5 After re-drying 3.3 51 55 53.0

[0078] (Reference Example 9) Briquettes were produced in the same manner as in Reference Example 7 except that a mixture was prepared with 15 parts by weight of the aqueous binder solution and 23.5 parts by weight of water with respect to 100 parts by weight of carbonized coal for a blending ratio of the aqueous binder solution, water, and carbonized coal based on the weight, and then measurements were performed. The results are shown in Table 11.

[0079] [Table 11] Blending ratio of Immersion time Moisture content Crushing strength (N)

1.5partsbyweight (minute) (% by weight) 1 2 Average Before drying 29.8 103 | 97 100.0 After drying 2.9 135 121 128.0 After immersion 1 5.4 153 141 147.0 After immersion 30 12.9 152 130 141.0 After immersion 1440 29.6 103 98 100.5 After re-drying 3.7 101 102 101.5

[0080] (Reference Example 10) Briquette were produced in the same manner as in Reference Example 7 except that a mixture was prepared with 20 parts by weight

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of the aqueous binder solution and 19 parts by weight of water with respect to 100 parts by weight of carbonized coal for a blending ratio of the aqueous binder solution, water, and carbonized coal based on the weight, and then measurements were performed. The results are shown in Table 12.

[0081] [Table 12] Blending ratio of Immersion time Moisture content Crushing strength (N)

(minute) (% by weight) 1 2 Average 2partsbyweight Before drying 27.1 118 110 | 114.0 After drying 4.2 153 155 154.0 After immersion 1 5.6 173 176 174.5 After immersion 30 7.9 142 146 144.0 After immersion 1440 23.5 108 123 115.5 After re-drying 3.6 114 135 124.5

[0082] FIG. 5 is a semi-logarithmic graph showing a relationship between an immersion time and a crushing strength of the briquettes of Reference Examples 6 to 10. It was confirmed that a crushing strength increased as a content of polyvinyl alcohol increased. It was confirmed that it was required to set a ratio of polyvinyl alcohol to 100 parts by weight of carbonized coal to 1.5 parts by weight or more in order to make a crushing strength 100 N or more both before and after immersion in water.

[0083] [Multiple addition of polyvinyl alcohol and a-starch] (Reference Example 11) An aqueous solution of a polyvinyl alcohol containing a polyvinyl alcohol (degree of saponification: > 99 mol%, degree of polymerization: 4,000) at a concentration of 10% by weight, a-starch used in Comparative Example 1-1, water, and the carbonized coal used in Example 1 were mixed to obtain a mixture. A blending ratio based

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on the weight in this case was 10 parts by weight for the aqueous solution of a polyvinyl alcohol, 1 part by weight for a-starch, and 28 parts by weight for water, with respect to 100 parts by mass of the carbonized coal. Briquette were produced in the same manner as in Example 2 except that this mixture was used, and then measurements were performed. The results are shown in Table 13.

[0084] [Table 13] Blending ratio of Immersion time Moisture content Crushing strength (N)

1pa-stareight (minute) (% by weight) 1 2 Average Before drying 27.2 58 61 59.5 After drying 4.4 88 103 95.5 After immersion 1 9.8 91 81 86.0 After immersion 30 18.7 73 64 68.5 After immersion 1440 32.5 66 59 62.5 After re-drying 3.0 80 92 86.0

[0085] (Reference Example 12) Briquette were produced in the same manner as in Reference Example 11 except that a mixture was prepared with 10 parts by weight of the aqueous solution of a polyvinyl alcohol, 3 parts by weight of a-starch, and 28 parts by weight of water with respect to 100 parts by weight of carbonized coal for a blending ratio of the aqueous solution of a polyvinyl alcohol, a-starch, water, and carbonized coal based on the weight, and then measurements were performed. The results are shown in Table 14.

[0086] [Table 14] Blending ratio of Immersion time Moisture content Crushing strength (N)

3apartsyweight (minute) (% by weight) 1 2 Average Before drying 27.8 45 44 44.5 After drying 4.3 160 164 162.0 After immersion 1 13.4 105 154 129.5 After immersion 30 26.3 84 61 72.5 After immersion 1440 35.8 52 61 56.5 After re-drying 2.7 141 139 140.0

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[0087] (Reference Example 13) Briquettes were produced in the same manner as in Reference Example 11 except that a mixture was prepared with 10 parts by weight of the aqueous solution of a polyvinyl alcohol, 5 parts by weight of a-starch, and 28 parts by weight of water with respect to 100 parts by weight of carbonized coal for a blending ratio of the aqueous solution of a polyvinyl alcohol, a-starch, water, and carbonized coal based on the weight, and then measurements were performed. The results are shown in Table 15.

[0088] [Table 15] Blending ratio of Immersion time Moisture content Crushing strength (N) a-starch (minute) (% by weight) 1 2 Average parts byweight ___________ ______

[0089] FIG. 6 is a semi-logarithmic graph showing a relationship between an immersion time and a crushing strength of the briquettes of Reference Examples 11 to 13. FIG. 7 is a graph which plots data of the briquettes of Reference Example 8 and Reference Examples 11 to 13 before being immersed (after being dried) and after being immersed for 24 hours (1,440 minutes) in water with a crushing strength as a vertical axis and a blending ratio (part by weight) of a-starch as a horizontal axis. Based on these pieces of data, it was confirmed that although adding of a-starch did not improve water resistance, a crushing strength of the briquette before immersion (after drying) in water and after re-drying could be significantly increased.

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[0090] [Influence of immersion time] (Example 14) Briquettes were produced in the same manner as in Example 2 except that a polyvinyl alcohol (degree of saponification: > 99.7 mol%, degree of polymerization: 1,700) was used instead of the polyvinyl alcohol used in Example 2, and then measurements were performed. Immersion in water was performed for 72 hours at maximum. The results are shown in Table 16.

[0091] [Table 16] Moisture content Crushing strength (N) Immersion time (%) 1 2 Average Before drying| 38.0 30 29 29.5 After drying 3.3 133 137 135.0 After immersion For 1 minute 11.3 133 144 138.5 After immersion For 10 minutes 24.6 109 104 106.5 After immersion For 30 minutes 27.8 79 85 82.0 After immersion For 60 minutes 30.3 75 84 79.5 After immersion For 24 hours 34.8 77 97 87.0 After immersion For 48 hours 37.5 79 76 77.5 After immersion For 72 hours 40.0 76 74 75.0 After re-drying 2.8 140 149 144.5

[0092] As shown in Table 16, it was confirmed that although a crushing strength decreased at the beginning of immersion in water, the crushing strength hardly decreased when an immersion time was longer than 30 minutes. Based on these results, it is also possible to simply evaluate a crushing strength after immersion for 24 hours with an immersion time set to 30 minutes.

[0093] (Comparative Example 4) Briquette were produced in the same manner as in Example 2 except that a polyvinyl alcohol (degree of saponification: 87 to 88 mol%, degree of polymerization: 1,700) was used instead of the

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polyvinyl alcohol used in Example 2, and then measurement was performed. The results are shown in Table 17.

[0094] [Table 17] Immersion time Moisture content 1 Crushing strength (N) (minute) (% by weight) 1 2 1 Average Before drying 38.6 4 4 | 4.0 After drying 2.6 38 40 39.0 After immersion | 1

[0095] The briquettes collapsed in less than a minute after being immersed in water. Accordingly, it was not possible to measure a crushing strength after immersion in water.

[0096] (Comparative Example 4) Briquettes were produced in the same manner as in Example 2 except that a polyvinyl alcohol (degree of saponification: 98.0 to 99.0 mol%, degree of polymerization: 1,700) was used instead of the polyvinyl alcohol used in Example 2. A crushing strength of the produced briquettes (after drying and after immersion in water at 20°C for 24 hours) was measured by the same procedure as in Example 2. The results are shown in Table 18. Table 18 also shows the results of Comparative Example 2, Comparative Example 3, Example 2, and Example 3.

[0097] [Table 18] Comparative Comparative Comparative Example Example Example 3 Example 2 Example 4 3 2 Degree of 1700 1700 1700 1700 1700 Polyvinyl polymerization alcohol Degree of saponification 87.0 to 89.0 94.5 to 95.5 98.0 to 99.0 > 99.3 > 99.85 (mol%) Crushing After drying 12.5 15.0 30.0 116.5 172.0 strength After immersion 0 0 6 73.5 96.0 (N) (for 24 hours)

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[0098] As shown in Table 18, Comparative Example 4 had only a slightly higher crushing strength than Comparative Examples 2 and 3. On the other hand, in Examples 2 and 3 in which a polyvinyl alcohol having a degree of saponification within the range of more than 99.3 mol%, a crushing strength after drying and after immersion in water was remarkably higher than those of Comparative Examples 2 to 4. In each of these examples and comparative examples, a polyvinyl alcohol was blended in a ratio of 3 parts by weight to 100 parts by weight of carbonized coal. It was confirmed that even when a blending ratio of a polyvinyl alcohol was low as described above, a high crushing strength could be obtained by using a polyvinyl alcohol having a high degree of saponification and a degree of polymerization of a predetermined value or more. Industrial applicability

[0099] According to the present disclosure, a production method for a briquette that has excellent safety and can maintain high strength even when it is wet with water is provided. Furthermore, a briquette that can maintain high strength even when it is wet with water is provided. Reference Signs List

[0100] 10: Measuring device, 14: Movable plate, 16: Briquette, 17: Support plate, 18: Stand

Claims

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[Claim 1] A production method for a briquette, the method comprising: a step of agglomerating an agglomerating raw material containing carbonized coal in powder form and a binder and drying at 60 0C to 100 0C to obtain the briquette having a moisture content of 5% by weight or less, wherein the binder contains an aqueous solution of a polyvinyl alcohol having a degree of saponification of more than 99.3 mol% and a degree of polymerization of 1,700 or more, and the carbonized coal in powder form is fine coal obtained by drying and carbonizing coal containing at least one of lignite and subbituminous coal.
[Claim 2] The production method for the briquette according to claim 1, wherein a degree of polymerization of the polyvinyl alcohol is 2,500 or more.
[Claim 3] The production method for the briquette according to claim 1 or 2, wherein a content of the polyvinyl alcohol in the aqueous solution is 1% to 10% by weight.
[Claim 4] The production method for the briquette according to any one of claims 1 to 3, wherein a content of the polyvinyl alcohol with respect to 100 parts by weight of the carbonized coal is 1 part by weight or more.
[Claim 5]

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The production method for the briquette according to any one of claims 1 to 4, wherein the binder contains a-starch.
[Claim 6] The production method for the briquette according to any one of claims 1 to 5, wherein a crushing strength of the briquette after being immersed in water at 20°C for 24 hours is 50 N or more.
[Claim 7] The production method for the briquette according to any one of claims 1 to 6, wherein neither calcium oxide nor magnesium oxide are added to the agglomerating raw material.