Comprehensive Fractal Description of Porosity of Coal of Different Ranks

Abstract

We selected, as the objects of our research, lignite from the Beizao Mine, gas coal from the Caiyuan Mine, coking coal from the Xiqu Mine, and anthracite from the Guhanshan Mine. We used the mercury intrusion method and the low-temperature liquid nitrogen adsorption method to analyze the structure and shape of the coal pores and calculated the fractal dimensions of different aperture segments in the coal. The experimental results show that the fractal dimension of the aperture segment of lignite, gas coal, and coking coal with an aperture of greater than or equal to 10 nm, as well as the fractal dimension of the aperture segment of anthracite with an aperture of greater than or equal to 100 nm, can be calculated using the mercury intrusion method; the fractal dimension of the coal pore, with an aperture range between 2.03 nm and 361.14 nm, can be calculated using the liquid nitrogen adsorption method, of which the fractal dimensions bounded by apertures of 10 nm and 100 nm are different. Based on these findings, we defined and calculated the comprehensive fractal dimensions of the coal pores and achieved the unity of fractal dimensions for full apertures of coal pores, thereby facilitating, overall characterization for the heterogeneity of the coal pore structure.

Effects of Liquid CO2 Phase Transition Fracturing on Mesopores and Micropores in Coal

“…We used a Micromeritics Autopore ASAP 2460 adsorption instrument to carry out the LTNA and LTCA experiments in saturated liquid nitrogen at a temperature of 77 K. It needs the coal samples with 60–80 mesh by crushing and screening. The BET theory can be employed to analyze the pore area, and the BJH theory can be adopted to derive the pore volume and pore size distribution. , …”

Comprehensive Fractal Model and Pore Structural Features of Medium- and Low-Rank Coal from the Zhunnan Coalfield of Xinjiang, China

“…The pore volume ratio of different pore diameter segments is used as the weight value to quantitatively characterize the complexity of the coal structure and its surface roughness. The fractal dimension of different pore diameter segments is weighted and summed [34] to obtain the comprehensive fractal dimension:…”

Effect of Division Methods of the Adsorption Isotherm on the Fractal Dimension of Clay Minerals Calculated Based on the Frenkel–Halsey–Hill Model

“…Based on the observation of the FHH model fitting lines on the adsorption isotherms in different samples, ,− it is found that there is no uniform method for dividing the adsorption isotherms when this model was applied. Moreover, the division method has great effect on the calculation result of the fractal dimension.…”

“…Type 2 , has two linear stages, and there was a transition region between the two stages (Figure e). Type 3 has three or more linear stages (Figure f). − Type 4 has no linear stage (Figure g) . In essence, method III takes the degree of linearity of the data processed by the FHH model as the selection principle for the range of isothermal adsorption data in order to obtain a reasonable fractal dimension.…”