1 Description Title of Invention: METHOD FOR PRODUCING MODIFIED COAL Technical Field (0001] The present invention relates to a method for producing upgraded coal and is effectively applicable particularly to a case of obtaining upgraded coal by upgrading low-rank coal (low-quality coal) having a high water content such as lignite or sub-bituminous coal. Background Art [0002] Despite large reserves, low-rank coal (low-quality coal) having a high water content such as lignite or sub-bituminous coal has a low calorific value per unit weight and poor transport efficiency. Accordingly, such low-rank coal is subjected to a heat treatment for drying in order to increase the calorific value per unit weight, and is also subjected to compression molding in order to improve a handling performance. [0003] Meanwhile, the low-quality coal subjected to the heat treatment is prone to water absorption. Moreover, such low-rank coal subjected to the heat treatment is prone to a reaction with oxygen existing in the air because of increased surface activity due to generation of radicals and the like on the surface along release of carboxylic groups and the like from the surface. Therefore, the low-rank coal has a risk of spontaneous H:\DYB\Intnvovcn\NRPonbKlDCC\DYB\5755229_l.doc-4/l112013 2 ignition due to a reaction heat associated with the reaction. [0004] In this context, Patent Literature I listed below or the like, for example, proposes a technique for upgrading low-quality coal to prevent spontaneous ignition of the coal by drying the low-quality coal (150'C) and dry-distilling the coal (250C to 450'C) to separate tar, then cooling the dry-distilled coal (200'C or below) and adding the tar to the dry-distilled coal to coat the dry-distilled coal with the tar. Citation List Patent Literature [0005] Patent Literature 1: Japanese Patent Application Publication No. Sho 60-063293. Summary of Invention Technical Problem [0006] However, the invention described in the above-mentioned Patent Literature 1 or the like is configured to add a volatile component such as the tar, which is separated and collected by dry distillation for different use, back to the dry-distilled coal. Therefore, the volatile component such as the tar, which is purposely separated and collected, cannot be used fully efficiently for other applications. [0007] In view of the above, the present invention aims to provide a method for producing upgraded H:\DYB\lntcnvovenNRPIonbl\CC\DYB\5755229_I.dc4/ll 2013 3 coal which can prevent spontaneous ignition at low cost without using a volatile component such as tar which is separated and collected by dry distillation. Solution to Problem [0008] A method for producing upgraded coal according to a first invention for aiming to solve the aforementioned problem is characterized in that the method comprises: a drying step of drying coal to obtain dried coal; a dry distillation step of dry-distilling the dried coal obtained in the drying step to obtain dry-distilled coal; a mixing step of mixing the dry-distilled coal obtained in the dry distillation step with fine powder coal generated and collected in association with the drying in the drying step; and a compression molding step of compression molding mixed coal obtained by the mixing in the mixing step to obtain upgraded coal. [0009] A method for producing upgraded coal according to a second invention is characterized in that, in the first invention, the mixing step is a step of mixing the dry distilled coal with the fine powder coal while adjusting proportions thereof so as to satisfy the following Formula (1) : 0.3 < B/A < 0.9 (1), where A is a proportion of a volatile component in the dried coal, and B is a proportion of a volatile component in the upgraded coal. [0010] 4 A method for producing upgraded coal according to a third invention is characterized in that, in the first invention, the mixing step is a step of further mixing leaked coal being leaked out and collected before being dried in the dried step. [00111 A method for producing upgraded coal according to a fourth invention is characterized in that, in the third invention, the mixing step is a step of mixing the dry-distilled coal, the fine powder coal, and the leaked coal while adjusting proportions thereamong so as to satisfy the following formula (1): 0.3 B/A 0.9 (1), where A is a proportion of a volatile component in the dried coal and B is a proportion of a volatile component in the upgraded coal. [0012] A method for producing upgraded coal according to a fifth invention is characterized in that, in any of the first to the fourth inventions, a compression molding temperature in the compression molding step is lower than a dry distillation temperature in the dry distillation step. [0013] A method for producing upgraded coal according to a sixth invention is characterized in that, in any of the first to the fifth inventions, the fine powder coal has an average grain size of 200 pm or smaller. [0014] H:\DYB\Intenvovcn\NRPorlbl\DCC\DYB\5755229_1.doc4/l1/2013 5 A method for producing upgraded coal according to a seventh invention is characterized in that, in any of the first to the sixth inventions, the coal is low-rank coal. Upgraded coal according to an eighth invention, when obtained by the method according to any one of the first to the seventh inventions. Advantageous Effects of Invention [0015] According to the method for producing upgraded coal of the present invention, the fine powder coal having been collected in the drying step and disposed of previously, which contains almost the same volatile component as the dried coal, is mixed with the dry-distilled coal. Hence it is not at all necessary to add any volatile components separated and collected by dry-distilling the dried coal back to the upgraded coal, so that the entire volatile component separated and collected by dry distillation can be used for other applications efficiently. Therefore, it may be possible to prevent spontaneous ignition at low cost without using the volatile component separated and collected by dry distillation, and to achieve further cost reduction because the fine powder coal that has been previously disposed of can be used efficiently. Brief Description of Drawings [0016] [Fig. 1] Fig. 1 is a process flowchart of a first embodiment of a method for producing upgraded coal according to the present invention. [Fig. 2] Fig. 2 is a process flowchart of a second embodiment of a method for producing upgraded coal according to the present invention.
6 Description of Embodiments [0017] Embodiments of a method for producing upgraded coal according to the present invention will be described below based on the accompanying drawings. It is to be noted, however, that the present invention will not be limited only to the embodiments to be described below based on the drawings. [0018] <First Embodiment> A first embodiment of a method for producing upgraded coal according to the present invention will be described based on Fig. 1. [0019] As shown in Fig. 1, a method for producing upgraded coal according to this embodiment is configured to perform: a drying step Sl of drying low-rank coal (low-quality coal) 1 to obtain dried coal 2; a dry distillation step S2 of dry-distilling the dried coal 2 obtained in the drying step Sl to obtain dry-distilled coal 5; a mixing step S3 of mixing the dry-distilled coal 5 obtained in the dry distillation step S2 with fine powder coal 3 generated and collected in association with the drying in the drying step Sl; and a compression molding step S4 of compression molding mixed coal 6 obtained in the mixing in the mixing step S3 to obtain upgraded coal 7. [0020] The low-quality coal 1 is the coal having a high water content (60% to 70%) such as lignite or 7 sub-bituminous coal. Although there are large reserves thereof, this coal has a low calorific value per unit weight and poor transport efficiency. [0021] The drying step Sl is the step of removing water 8 from the low-quality coal 1, in which the dried coal 2 adjusted to the water content of nearly 0% is produced by supplying the low-quality coal 1 to a hot air dryer or the like of a belt conveyor type or the like, for example, and by drying the coal with hot air (100 0 C to 280 0 C (preferably 150 0 C to 2000C)). [00221 Here, in the hot air drying process, fine powder coal 3 (an average grain size: about 200 pm or smaller) is generated in association with the drying and is taken out and discharged to the atmosphere together with the hot air. Therefore, the fine powder coal 3 is collected from the hot air by using fine powder collecting means such as a cyclone separator or a filter installed at an exhaust air duct of the hot air dryer. [0023] The dry distillation step S2 is the step of removing a volatile component 9 such as tar from the dried coal 2, in which the dry-distilled coal 5 is produced by supplying the dried coal 2 to a continuous dry distiller, for example, and dry-distilling the dried coal 2 at a high temperature (300 0 C to 500 0 C (preferably 400'C to 450 0 C)) to separate and collect the volatile component 9 such as tar. [0024] 8 The mixing step S3 is the step of mixing the fine powder coal 3 with the dry-distilled coal 5, the fine powder coal 3 being collected from the hot air from the hot air dryer or the like in the drying step Sl. In the mixing step S3, the mixed coal 6 is produced by supplying the fine powder coal 3 collected by the collecting means and the dry-distilled coal 5 together into a mixer and agitating the mixture uniformly. [0025] At this time, assuming that a proportion of the volatile component 9 in the dried coal 2 is A and that a proportion of the volatile component 9 in the upgraded coal 7 is B, it is preferable to mix the dry-distilled coal 5 and the fine powder coal 3 together, while proportions thereof are adjusted so that a ratio of the proportion B relative to the proportion A (B/A) can be between 0.3 and 0.9 (0.3 B/A 0.9 ... Formula (1)) or between 0.5 and 0.7 (0.5 B/A 0.7) in particular. [0026] Here, the proportion (A) of the volatile component 9 in the dried coal 2 is a value to be obtained in advance by a chemical composition analysis prior to the mixing, and a proportion of the volatile component 9 in the fine powder coal 3 has almost the same value as the proportion (A) of the volatile component 9 in the dried coal 2 in substance. Meanwhile, a proportion (C) of the volatile component 9 in the dry-distilled coal 5 has a value, which can be preset prior to the mixing depending on dry distillation conditions including a dry distillation temperature, dry distillation time, and 9 the like, and is obtained accurately by a chemical composition analysis prior to the mixing. Moreover, the proportion (B) of the volatile component 9 in the upgraded coal 7 is a value which is preset prior to the mixing depending on properties and the like required for the upgraded coal 7. [0027] In the compression molding step S4, the mixed coal 6 is compressed (1200 kg/cm 2 x 300*C to 450 0 C (preferably 350 0 C to 4000C)) and molded into solid briquettes of a columnar shape, a ball-like shape, or the like, so that the upgraded coal 7 is produced accordingly. The mixed coal 6 has been obtained by mixing the dry-distilled coal 5 with the fine powder coal 3, the dry-distilled coal 5 undergoing separation and removal of the volatile component 9 such as the tar and thereby containing a very small amount of the volatile component 9, the fine powder coal 3 intrinsically containing the volatile component 9 such as the tar. [0028] The upgraded coal 7 thus produced is molded so as to evenly include the volatile component 9 such as the tar contained in the fine powder coal 3 on the whole. Thus, spontaneous ignition is prevented, while the strength of the upgraded coal 7 as a molded product is enhanced. [0029] In short, whereas spontaneous ignition of the upgraded coal has previously been prevented by adding 10 the volatile component obtained by dry-distilling the dried coal back to dry-distilled coal, this embodiment is configured to prevent spontaneous ignition of the upgraded coal 7 by mixing the dry-distilled coal 5 with the fine powder coal 3, which has been collected in the drying step Sl and previously disposed of and contains almost the same volatile component 9 as that in the dried coal 2. [0030] Accordingly, this embodiment enables prevention of spontaneous ignition of the upgraded coal 7 by use of the fine powder coal 3 which has previously been disposed of. Hence it is not at all necessary to add the volatile component 9 separated and collected by dry-distilling the dried coal 2 back to the upgraded coal 7, so that the entire volatile component 9 separated and collected by dry distillation can be used for other applications efficiently. [0031] Therefore, according to this embodiment, it is possible to prevent spontaneous ignition at low cost without using the volatile component 9 separated and collected by dry distillation, and to achieve further cost reduction because the fine powder coal 3 that has been previously disposed of can be used efficiently. [0032] As described above, on the assumption that a proportion of the volatile component 9 in the dried coal 2 is A and that a proportion of the volatile component 9 in the upgraded coal 7 is B, the dried coal 5 and the 11 fine powder coal 3 are mixed together, while proportions thereof are adjusted so that a ratio of the proportion B relative to the proportion A (B/A) can be between 0.3 and 0.9 (0.3 B/A 0.9 ... Formula (1)) or between 0.5 and 0.7 (0.5 B/A 0.7) in particular. This makes it possible not only to prevent spontaneous ignition but also to increase a crushing load on the upgraded coal 7 to a necessary and sufficient size (around 50 kg) . Thus a handling performance of the upgraded coal 7 can be substantially improved. [0033] Moreover, depending on the amount of the fine powder 3 to be mixed, it is possible to separate and collect the volatile component 9 in the dry-distilled coal 5 as much as possible by setting the dry distillation temperature as high as possible. Hence the amount of the volatile component 9 available for efficient use in other applications can be increased further. [0034] Note that a compression molding temperature Tp in the compression molding step S4 is preferably lower than a dry distillation temperature Td in the dry distillation step S2 (Tp < Td), because the volatile component 9 may be removed by evaporation at the time of compression molding and the proportion of the volatile component 9 in the upgraded coal 7 may drop when the compression molding temperature Tp is higher than the dry distillation temperature Td. [0035] 12 <Second Embodiment> A second embodiment of the method for producing upgraded coal according to the present invention will be described based on Fig. 2. It is to be noted, however, that similar portions to those in the case of the above-described first embodiment will be designated by similar reference numerals to the reference numerals used in conjunction with the explanation of the above-described first embodiment, whereby duplicate explanation of the explanation in the above-described first embodiment will be omitted. [0036] As shown in Fig. 2, a method for producing upgraded coal according to this embodiment is configured to perform: a drying step S1 of drying low-rank coal (low-quality coal) 1 to obtain dried coal 2; a dry distillation step S2 of dry-distilling the dried coal 2 obtained in the drying step Sl to obtain dry-distilled coal 5; a mixing step S13 of mixing the dry-distilled coal 5, fine powder coal 3, and leaked coal 4 together, the dry-distilled coal 5 being obtained in the dry distillation step S2, the fine powder coal 3 generated and collected in association with the drying in the drying step Sl, the leaked coal 4 leaked and collected before being dried in the drying step Sl; and a compression molding step S4 of compression molding mixed coal 16 obtained by the mixing in the mixing step S13 to obtain upgraded coal 7. [0037] 13 The leaked coal 4 is the coal leaked out of a hot air dryer or the like of a belt conveyor type or the like, for example, when the coal is supplied to the dryer and is collected without being dried completely in the drying step Sl. The leaked coal 4 has previously been disposed of. [0038] The mixing step S13 is the step of mixing the dry-distilled coal 5 with the leaked coal 4 leaked out of the dryer and collected in the drying step Sl as well as the fine powder coal 3 collected from the hot air in the drying step Sl. The mixed coal 16 is produced by supplying the fine powder coal 3 and the leaked coal 4 into a mixer together with the dry-distilled coal 5 and by agitating the mixture uniformly. [0039] At this time, as described above, assuming that a proportion of the volatile component 9 in the dried coal 2 is A and that a proportion of the volatile component 9 in the upgraded coal 7 is B, it is preferable to mix the dry-distilled 5, the fine powder coal 3, and the leaked coal 4 together, while proportions thereof are adjusted so that a ratio of the proportion B relative to the proportion A (B/A) can be between 0.3 and 0.9 (0.3 B/A 0.9 ... Formula (1) ) or between 0.5 and 0.7 (0.5 B/A 0.7) in particular. [0040] Note that although the leaked coal 4 contains the water 8, the water 8 is evaporated and almost eliminated at the time of compression molding. Accordingly, a 14 proportion of the volatile component 9 in the leaked coal 4 becomes almost equal to a value (A) after deduction of the contained water 8, or namely, the proportion (A) of the volatile component 9 in the dried coal 2 in substance. [0041] Subsequently, in the compression molding step S4, the mixed coal 16 is compressed (1000 kg/cm 2 to 2000 kg/cm 2 x 300*C to 4000C (preferably 3500C to 4000C)) and molded into solid briquettes of a columnar shape, a ball-like shape, or the like, so that the upgraded coal 7 is produced accordingly. The mixed coal 16 has been obtained by mixing the dry-distilled coal 5 with the fine powder coal 3 and the leaked coal 4, the dry-distilled coal 5 undergoing separation and removal of the volatile component 9 such as the tar and thereby containing a very small amount of the volatile component 9, the fine powder coal 3 intrinsically containing the volatile component 9 such as the tar. [0042] The upgraded coal 7 thus produced is molded so as to evenly include the volatile component 9 such as the tar contained in the fine powder coal 3 on the whole, as similar to the case of the aforementioned embodiment. Thus, spontaneous ignition is prevented, while the strength of the upgraded coal 7 as a molded product is enhanced. [0043] The aforementioned embodiment is configured to achieve prevention or the like of spontaneous ignition 15 of the upgraded coal 7 by mixing the dry-distilled coal 5 with the fine powder coal 3, which has been collected in the drying step S1 and previously disposed of and contains almost the same volatile component 9 as that in the dried coal 2. On the other hand, this embodiment is configured to achieve prevention or the like of spontaneous ignition of the upgraded coal 7 by collecting the leaked coal 4 as well which has been leaked out before being dried in the drying step Sl and previously disposed of and contains almost the same volatile component 9 as that in the dried coal 2, and by further mixing the leaked coal 4 with the dry-distilled coal 5. [0044] Therefore, according to this embodiment, it is possible not only to achieve effects similar to the case of the above-described embodiment but also to achieve prevention or the like of spontaneous ignition of the upgraded coal 7 by further making efficient use of the leaked coal 4 that has previously been disposed of. Hence this embodiment can achieve further cost reduction as compared to the aforementioned embodiment. [0045] Moreover, as described above, on the assumption that a proportion of the volatile component 9 in the dried coal 2 is A and that a proportion of the volatile component 9 in the upgraded coal 7 is B, the dry-distilled coal 5, the fine powder coal 3, and the leaked coal 4 are mixed while proportions thereof are 16 adjusted so that a ratio of the proportion B relative to the proportion A (B/A) can be between 0.3 and 0.9 (0.3 B/A 0.9 ... Formula (1)) or between 0.5 and 0.7 (0.5 B/A 0.7) in particular.. This makes it possible not only to prevent spontaneous ignition but also to increase the crushing load on the upgraded coal 7 to the necessary and sufficient size (around 50 kg) as similar to the case of the above-described embodiment. Thus the handling performance of the upgraded coal 7 can be substantially improved. Industrial Applicability [0046] A method for producing upgraded coal according to the present invention can prevent spontaneous ignition at low cost without using a volatile component separated and collected by dry distillation and also make efficient use of fine powder coal which has previously been disposed of so as to achieve further cost reduction. Therefore, the method is very useful industrially. Reference Signs List [0047] 1 LOW-RANK COAL (LOA-QUALITY COAL) 2 DRIED COAL 3 FINE POWDER COAL 4 LEAKED COAL 5 DRY-DISTILLED COAL 6, 16MIXED COAL 7 UPGRADED COAL 8 WATER H:\DYBInterwoven\NRPorb\DCC\DYB\5755229_1.doc-4I l2013 17 9 VOLATILE COMPONENT Sl DRYING STEP S2 DRY DISTILLATION STEP S3,S13 MIXING STEP S4 COMPRESSION MOLDING STEP Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.