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1968年美国煤炭总产量为545百万吨,其中送往炼焦的约95百万吨。美国原煤质量的趋向是灰分提高和末煤大幅度增加。美国选煤厂的入洗原煤灰分平均为25%,精煤灰分在7%以上。约有70%的原煤经过分选。虽然入选原煤量增加了,但是由于选煤厂平均生产能力增大,厂数反而减少了(1960年全国有洗煤厂612座,至1967年降至471座)。
In 1968, total coal production in the United States was 545 million tons, of which about 95 million tons were sent to coking. The trend of coal quality in the United States is the increase of ash and the increase of terminal coal. The average coal ash content of the United States coal preparation plant is 25% and the ash content of the fine coal is above 7%. About 70% of the coal is sorted. Although the amount of raw coal selected increased, the number of plants decreased due to the increase in the average capacity of the coal preparation plant (in 1960, there were 612 coal washing plants in the country and 471 in 1967).