Pore structure and its impact on CH4 adsorption capacity and flow capability of bituminous and subbituminous coals from Northeast China

• Published in: Fuel (Guildford) 2013-01, Vol.103, p.258-268
• Main Authors: Cai, Yidong, Liu, Dameng, Pan, Zhejun, Yao, Yanbin, Li, Junqian, Qiu, Yongkai
• Format: Article
• Language: English
• Subjects: Adsorption; Applied sciences; Bituminous and subbituminous coals; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Flow; Fuels; Pore structure
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2012.06.055

► An integrated approach to characterize PS/VD distribution for coals is proposed. ► SAXS shows the micropores less than 10nm consist over 90% of micropores volume. ► Micropore (2–5nm) has greater impact on CH4 adsorption than that of mesopore. ► Smooth surface of coal pores (r>10nm) is also favorable for CH4 adsorption. Adsorption-pore (pore size less than 100nm) and seepage-pore (pore size greater than 100nm) structures have great effects on gas adsorption/diffusion and gas flow in coal seam, respectively. Pore properties, including porosity, size/volume distribution, volumes, surface fractals, specific surface area, and connectivity, for four coals from Northeast China were acquired through mercury porosimetry, N2 adsorption at 77K, small angle X-ray scattering (SAXS) and their relationships with CH4 adsorption capacity and permeability are investigated. The roughness of pore surface was analyzed with surface fractal dimensions. Obtained values of fractal dimensions from mercury porosimetry and N2 adsorption at 77K were comparable with values determined by SAXS measurement. The surface fractals results show that the more irregular surface, the more inhomogeneous pore structures is, meaning more surface area and then stronger adsorption capability, especially for the micropores with sizes in the range of 2–10nm and the mesopores. Moreover, with the data of petrographic, proximate and ultimate analyses, the ratio of C/H, moisture content, ash yield also have great effects on CH4 adsorption capacity of coals. For bituminous and subbituminous coals, macropores have significant impacts on gas flow. The coals with high contents of macroporosity generally have good gas flow capability. Therefore, they may have significant implications for coalbed methane (CBM) exploitation.