It has been described that coal was discovered at Miike, Japan in 1465.In Edo era, Miike mine had been operated systematically for 150 years.
A westernized mining technology was introduced by the British in 1878. Mitsui Mining Company Limited succeeded the operation in 1889 and has continued it up to the present.
In spite of huge amount of coal resources and thick seam, Miike mine had been trou-bled with a gush of water and faced with a severe condition of the mining under the bot-tom of the sea since 1910. However, Miike mine has defeated these disadvantages with the constant efforts and the employment of new technologies, and has built up the pre-sent status accumulating the valuable experiences.
Miike mine has played an important roll of a leader in mining industries and has contributed to the society. Unfortunately, Miike mine has at last come to an end of the roll in 1997 for economical reason. In the history of 110 years, Mitsui mining company produced and supplied over 289 million tons of coal. Now we have a duty to look back the course Miike mine and Mitsui mining company have followed and achieved.

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Basic chracteristics of humic acids extracted from weathered coal (China) and tropical peat (Indonesia) were compared. The comparison was also made between the extraction of humic acid by conventional method (NaOH, NaOH/Na₄P₂O₇) and a new process using NH₄OH as an extractant. Regardless of the extractant, humic acid extracted from tropical peat has about four times as large average molecular weight as that from weathered coal. As for the functional groups, humic acid extracted from weathered coal has higher quantity of carboxyl group, but lower quantity of phenolic hydroxyl group.Humic acid extracted from weathered coal contains much aromatics in the structure.
The yield of the humic acid with NaOH was the highest among the three extractants. The humic acid extracted with NH₄OH contained a smaller amount of ash but a larger amount of ammoniacal nitrogen than with NaOH or NaOH/Na₄P₂O₇.
The cation exchange reactions of humic acid were accelerated by the higher electric charge of metal ions, the higher carboxyl group content and the lower molecular weight of the humate.

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The effects of solvent/coal ratio (S/C) and gas flow rate (GFR) on liquefaction reaction of Victorian brown coal were investigated using a process development unit (PDU) with three stirred tank reactors. For all experiments, the iron/sulfur catalyst (Fe₂O₃, S/Fe atomic ratio 1.2) was added 3wt.% as Fe and H2 gas was fed 10wt.% on moisture and ash free (maf) coal. The S/C (maf) ratio by weight in the feed slurry ranged from 2.0 to 3.0 and the gas in the gas-liquid separator was circulated to the first reactor to increase the GFR in the reactors.
The distillate yield (b. p.<420°C) and hydrogen efficiency increased with a decrease in the S/C at lower GFR condition without gas circulation. An increase in the GFR by the gas circulation markedly improved the distillate yield and hydrogen efficiency, effectively converting the heavier fraction derived from the coal to the distillate. This GFR effect was considerably greater than that of the S/C, and the S/C effects disappeared at higher GFR conditions. These results were explained by higher contents of the catalyst and heavy fraction in the liquid phase in the reactors under the conditions of lower S/C and higher GFR because the amounts of the added catalyst and fed H2 were fixed constant to the coal in the feed slurry. The increase in the GFR markedly accelerated the vaporization of solvent fraction and concentrated the catalyst and heavy fraction in the remaining liquid phase in the reactors. Thus, at higher GFR conditions, the actual residence time of the liquid phase in the reactors was prolonged and the liquefaction reaction was markedly enhanced.

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