Study of high-pressure sorption of methane on Chinese coals of different rank
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ORIGINAL PAPER
Study of high-pressure sorption of methane on Chinese coals of different rank Jian Shen & Yong Qin & Xuehai Fu & Geoff Wang & Run Chen & Lijuan Zhao
Received: 23 July 2013 / Accepted: 14 May 2014 # Saudi Society for Geosciences 2014
Abstract To investigate the sorption and diffusion behavior of deep coals, high-pressure sorption experiments of methane on coals were performed by the volumetric method. The experimental sorption isotherms fit the Langmuir model over the experimental pressure and temperature ranges. The sorption volumes of all coals tested exhibit a typical temperature behavior with a negative exponent decreasing as temperature increases. An approximately linear correlation for the methane Langmuir volume with coal rank was observed. The effect of coal rank on adsorption volume decreases with increasing temperature. The Langmuir pressure decreases initially with coal rank, reaches a minimum pressure corresponding to the maximum vitrinite reflectance at ∼2.2 % and then increases. Studies on the diffusion of methane in coal using a unipore diffusion model showed that the effective diffusion coefficients for the seven coals studied varied from 2.98 to 68.3× 10−5 s−1. The effective diffusion coefficients of coal at the first pressure step generally increased linearly with increasing temperature, and a complex nonlinear relationship for methane sorption rate with coal rank was observed. Finally, an empirical equation was developed to estimate the sorption capacity of methane on coal of a given rank as a function of the coal J. Shen : Y. Qin : X. Fu Key Laboratory of CBM Resources and Dynamic Accumulation Process, Ministry of Education of China, Xuzhou 221116, China J. Shen : R. Chen : L. Zhao Key Laboratory of Coal-based CO2 Capture and Geological Storage Jiangsu Province, Xuzhou 221116, China J. Shen (*) : Y. Qin : X. Fu : L. Zhao School of Resource and Earth Science, China University of Mining and Technology, Xuzhou 221116, China e-mail: [email protected] G. Wang School of Chemical Engineering, The University of Queensland, Brisbane, Queensland 4072, Australia
burial depth in a time-invariant pressure and temperature field. The sorption capacity of the moisture-equilibrated coal was found to increase with burial depth until it reaches a maximum of 24 cm3/g at ∼1,500 m, followed by a slow decline to 20.5 cm3/g at approximately 3,000 m. Keywords Chinese coal . Coalbed methane . High-pressure sorption . Diffusion . Sorption kinetics
Introduction In addition to mine safety, greenhouse gas (CH4, CO2) emissions associated with coal mining and the exploitation of coalbed methane (CBM) from coal seams is an important subject in the fields of coal and CBM. Emissions have become of increasing concern worldwide over the past two decades, especially in China (Zou et al. 2013; Li et al. 2014). The emission and recovery of methane from coals, which is controlled mainly by CBM content and its transport in coal, are related closely to the adsorption and diffusion behaviors of CBM (Meng et al. 2013)
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