Fractal characteristics of pulverized high volatile bituminous coals with different particle size using gas adsorption. (1st May 2022)

• Record Type: Journal Article
• Authors: Wang, Xiaoming; Dang, Zheng; Hou, Shihui; Yuan, Yudong; Wang, Xingjin; Pan, Sidong
• Is Part Of: Fuel. Volume 315(2022)
• Publication Date: 2022-05-01
• Subjects: Fractal dimension -- Pore characteristics -- Particle size fraction -- Low-pressure gas adsorption -- High volatile bituminous coal; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2021.122814
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: Crushing plays different roles in mesopore and micropore characteristics. Decreased particle size causes smooth pore surface and complicated pore structure. Mesopores with pore width of 2–5 nm are the key to fractal characteristics. Mesopore structure parameters have an important effect on fractal characteristics. Model for pore structure and gas molecules distribution is proposed. Abstract: To better understand the effect of particle size on fractal characteristics of pores in coal, three high volatile bituminous coals with mean maximum vitrinite reflectance of 0.82–0.90% collected from the Naryksko-Ostashinskaya coalbed methane field in Kuznetskiy Basin in Russia were crushed and sieved to five progressively decreasing particle size fractions: 1.0–0.5 mm, 0.50–0.25 mm, 0.250–0.125 mm, 0.125–0.063 mm and 0.063–0.032 mm. For all particle size fractions, particle size distribution measurement, proximate analysis, maceral analysis and low-pressure N2 adsorption and CO2 adsorption analyses were conducted. Fractal dimensions D1 (pore surface roughness) and D2 (pore structural irregularity) were determined from relative pressure intervals of 0–0.45 and 0.45–1 of N2 adsorption isotherm with the application of the fractal Frenkel-Halsey-Hill theory, respectively. The results demonstrate significant differences in fractal dimensions in different particle size fractions. As particle size of coal samples decreases, D1 decreases, while D2 increases. Some constricted mesopores are transformed into non-constricted mesopores during crushing. The non-constricted mesopores increasingly concentrate in smaller pore sizes, which results in smoother pore surface (decreasing D1 ) and more heterogeneous pore structure (increasing D2 ). Mesopores with pore width between 2 nm and 5 nm are the key to fractal dimensions. Individual mesopore structure parameters closely associated with particle size have universal correlations with fractal dimensions. The increasing mesopore specific surface area and volume and decreasing average mesopore width lead to a decrease in D1 and an increase in D2, which further confirms the effect of particle size on fractal dimensions.