Variation of Coal Permeability under Dehydrating and Heating: A Case Study of Ulanqab Lignite for Underground Coal Gasification

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• 作者：Shuqin Liu ; Shangjun Zhang ; Feng Chen ; Caihong Wang ; Mingyue Liu
• 刊名：Energy & Fuels
• 出版年：2014
• 出版时间：November 20, 2014
• 年：2014
• 卷：28
• 期：11
• 页码：6869-6876
• 全文大小：334K
• ISSN：1520-5029

文摘

Underground coal gasification (UCG) is a promising option for the recovery of low-rank and inaccessible coal resources, during which coal permeability plays an important role in various aspects, including the method of channel construction, fire face extension, and gas yield. In this paper, experimental studies were conducted examining the permeability of Ulanqab lignite from Inner Mongolia, northern China, with the focus being on the variation of coal permeability under dehydrating and heating below 400 掳C. In addition, the specific surface area and the pore volume of the heated samples were analyzed. The results indicate that the permeability of the lignite in the direction parallel to the bedding is 3 times greater than that observed perpendicular to the bedding, while the permeability values of three high-rank coals considered in this study exhibit the opposite trend. With a decrease in the water content of the lignite sample, the permeability exhibits an increasing 鈥淪-curved鈥?trend. The permeability of the coal sample in the as-received state (ARS) is determined to be nearly 100 times higher than that in the water-saturated state (WSS). When the ARS sample is heated to over 300 掳C, the permeability sharply increases and attains 2000 mD at 400 掳C, while the lowest value remains between 200 and 300 掳C. The temperature affects the permeability of lignite by changing the specific surface area and the pore volume. Draining, preheating, and high-pressure air fracturing are proposed as efficient methods for improving the permeability of the lignite regarding the UCG process.