低阶煤吸附孔特征及分形表征

doi:10.11743/ogg20180216

Abstract

Abstract: We collected 8 kinds of low rank coal (LRC) with distinguished macrolithotypes,carried out some experiments like the low-temperature liquid nitrogen adsorption and isothermal methane adsorption,discussed the LRC adsorption pore characteristics,and established the relationship between fractal model suitable for LRC adsorption pores and fractal dimension with pore structures and adsorption capacities.From this,the LRC absorption/desorption curves are divided into four categories with 4 corresponding pore types:taper-shaped pores with one end closed being dominant in bright coal,ink-bottle-shaped pores dominating semi-bright coal,open-cylindric pores and wedge-shaped ones occurring in semidull coal,and open-cylindric pores being predominant in dull coal.Results show that (1) compared with the BET model,the FHH model is more appropriate for the characterization of LRC pores in respect of fractal nature;(2) the various macrolithotypes in FHH model show different adsorption characteristics at relative pressure 0~0.5 and 0.5~0.5 and have fractal dimensions D₂₁ and D₂₂ respectively,with D₂₁ representing the surface roughness of adsorption pores and D₂₂ the irregularity of the pore structures.As D₂₁ gets bigger,the pore specific surface area increases,whereas the bigger D₂₂ gets,the smaller the average pore size becomes,the higher the micropore content is,and the larger the pore heterogeneity is;(3) D₂₁ is more effective than D₂₂ in controlling the adsorption capacity of LRC.When the coal is characterized by high D₂₁ and low D₂₂,the adsorption capacity is the strongest,and the adsorption capacity enlarges as the fractal dimension of cumulative specific surface area increases.The LRC adsorption process subsequently shows transition from predominance of monomolecular layer adsorption to predominance of polymolecular layer adsorption with increasing pressure.

Key words: specific surface area, FHH model, low-temperature liquid nitrogen adsorption, fractal dimension, pore structure, LRC

CLC Number:

TE132.2

Zhou Sandong, Liu Dameng, Cai Yidong, Yao Yanbin, Jiao Yongyan, Ren Shijun. Characterization and fractal nature of adsorption pores in low rank coal[J]. Oil & Gas Geology, 2018, 39(2): 373-383.

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Characterization and fractal nature of adsorption pores in low rank coal

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