Abstract
Coal bumps, coal and gas bursts are currently the main threats to coal mine safety in China. The physical properties of coal are important determining factors for the occurrence of coal bumps or coal and gas bursts. A series of experiments using mercury intrusion porosimetry (MIP), nitrogen adsorption (NA) and carbon dioxide adsorption (CA) were employed to investigate the pore size distributions (PSDs) of bump-prone coal and gas-outburst coal. Considering the influence of coal matrix compressibility on the MIP experimental data, the MIP data should be considered in combination with NA and CA testing data. The dominant pores of gas-outburst coal are different from those of bump-prone coal. The PSDs of coal samples have multifractal characteristics. However, the multifractal characteristics of two types of coal are different. (Answer to question 1, reviewer 2). A comparison of the multifractal parameters indicated that Xin Zhou Yao (XZY) coal samples have a higher spatial heterogeneity and complexity of their pore size distribution, while Zhao Ge Zhuang (ZGZ) coal samples have a lower heterogeneity and pore connectivity, which may hinder smooth gas flow and lead to a localized collection of gas in coal seams.
Highlights
Coal is the main energy source in China
The fractal dimensions are divided into the surface dimension (Ds) together with the volume fractal dimension according to different research purposes, mathematical equations and algorithms for which they are used during transforms
In combination with mercury intrusion porosimetry (MIP) data and N2 and CO2 adsorption data, Li analyzed the pore porosimetry based on different pore size distributions (PSDs) of three kinds of coals, the multifractal method was used to characterize the pore categories and the generalized spectra showed how to describe the differences among the different PSDs of coal[25]
Summary
Coal is the main energy source in China. With increases in the exploiting depth and intensity of coal mining in China, the occurrence of dynamic disasters, such as coal bumps or coal and gas outbursts, is increasingly frequent[1]. To investigate the pore structure of coals, a variety of effective methods such as mercury intrusion porosimetry (MIP), small angle X-ray scattering (SAXS), gas adsorption analysis (GAA), scanning electron microscope (SEM) and computed tomography (CT)[11,12,13,14,15,16] have been successfully applied These methods allow the pore size distribution to be obtained quantitatively, there is hardly an effective approach to calculate and conclude the data from the above methods for coal, which is a multi-porous material. By analyzing the data and noting the differences of the coal samples from different coal seams, this study calculates the multifractal singularity spectra and the generalized dimension spectra, which are significant parameters in characterizing the pore structure and important links between PSDs and dynamic disasters. These coal samples used for MIP, NA and CA testing are thought to be representative. (Answer to question 2 reviewer 1 and editor)
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