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煤是一种从地下挖掘出来的可燃烧的固体物质。它是由许多种复杂的化合物组成的混合物。它的化学成分,主要是碳,此外尚有氢、氧、氮、硫、磷等元素及各种矿物质等。在工业上,又分为水分、灰分、挥发分和固定碳四种成分。灰分是煤燃烧後剩下的残渣。挥发分是煤中含有的挥发性气体。挥发分和固定碳是可燃烧部分,灰分是不燃烧部分。可燃烧部分是有用部分,不燃烧部分和水分是废物,也是煤的不良的组成部分。煤经过燃烧後,可燃烧部分都烧掉了,水分蒸发,而各种矿物质则结成硬性的残渣,卽是灰分。煤是千百万年以前植物层在水底下积聚,隔绝了空气,经过碳化作用生成的。大约在二亿八千万到二亿二千万年以前的时期内,世界各地普遍造成煤层,地质学家把这个时期称为“石
Coal is a combustible solid material excavated from the ground. It is a mixture of many complex compounds. Its chemical composition is mainly carbon, in addition there are hydrogen, oxygen, nitrogen, sulfur, phosphorus and other elements and various minerals. In industry, it is divided into four components: water, ash, volatile matter, and fixed carbon. Ash is the residue left after the coal burns. Volatile gas is a volatile gas contained in coal. Volatile and fixed carbon are combustible parts and ash is an incombustible part. The combustible portion is a useful portion, the non-combustion portion and moisture are waste, and it is also a bad component of coal. After the coal has burned, the flammable parts are burned, the water evaporates, and the various minerals form a hard residue. The ash is ash. Coal is accumulated millions of years ago under the water, isolated from the air and formed by carbonization. About 280 million to 220 million years ago, coal seams were commonly found around the world. Geologists called this period “stone