Fractal characteristics of pore structures in 13 coal specimens: Relationship among fractal dimension, pore structure parameter, and slurry ability of coal

The fractal characteristics of pore structures in 13 different coal specimens were investigated. Insights into the relationship among fractal dimension, pore structure parameter, and slurry ability of coal were provided. N-2 adsorption/desorption at 77 K was applied to analyze the pore structure of coal. Two fractal dimensions, D-1 and D-2, at relative pressures of 0 to 0.45 and 0.45 to 1, respectively, were calculated with the fractal Frenkel-Halsey-Hill model. Results reveal that the value of D-1 is mainly affected by the influence of meso- and macro-pores with an average pore size range of 10 nm to 220 nm on the specific surface area; therefore, Di can be utilized to quantitatively describe the surface roughness of these meso- and macro-pores in coal. Meanwhile, the value of D-2 is mainly related to the effects of fine mesopores with an average pore size range of 2 nm to 10 nm on the total pore volume; therefore, D-2 can be utilized to quantitatively describe the volumetric roughness of these mesopores in coal. Di has no apparent linear correlation with the pore structure parameters and maximum solid loading of coal, and D-2 has a positive linear correlation with the specific surface area and total pore volume of coal. The increase in specific surface area, total pore volume, and D-1 has negative effects on the slurry ability of coal. High-rank coals with high ash content and low volatile matter relatively have higher Di and lower D-2. Meanwhile, with increasing coal rank, D-2 has a decreased trend. The fine mesopores with an average pore size range of 2 nm to 10 nm in coal have direct effects on the pore structure parameters and D-2 of coal; thus, the slurry ability of coal may be improved if the number of these mesopores in coal is reduced by modification processes, such as microwave irradiation, hydrothermal treatment and so on. (C) 2016 Elsevier B.V. All rights reserved.