The binary gas sorption in the bituminous coal of the Huaibei Coalfield in China

Abstract

Knowledge of the gas sorption characteristics of a coal not only helps to explain the mechanism of enhanced coalbed methane recovery but also provides an important basis for simultaneous coal and gas extraction. In consequence, the pure and binary gas excess sorption capacity of methane, carbon dioxide, and nitrogen of bituminous coal samples derived from the Xutuan Coal Mine in Huaibei coalfield, in Anhui Province in China, was measured using the volumetric method. The fitting analysis of the pure gas Langmuir adsorption model was carried out. The binary gas excess sorption measurement showed that the final sorption capacity of bituminous samples was the same no matter what the gas adsorption order of competitive adsorption and displacement adsorption. Hence, coal gas adsorption is physical adsorption, i.e. the different adsorption and desorption process of gas molecules does not affect the final adsorption amount of coal to each component of gas. Using the fitting parameters obtained by the Langmuir equation, the extended Langmuir equation was used to predict the adsorption capacity for each component of the binary gas. The comparison between predicted adsorption capacity and measured adsorption capacity showed that the extended Langmuir equation can better describe the trend of the adsorption isotherm curves of a binary gas under different pressures. The separation coefficient and displacement coefficient were defined from Langmuir adsorption theory. The separation coefficient involves the proportion of each component in the free phase and the proportion of each component in the adsorption phase. The displacement coefficient involves the displacement ability of gas molecules at adsorption sites by free gas molecules.

Experimental study on the seepage characteristics of bituminous coal under the conditions of liquid nitrogen fracturing

“…The main factors that affect the permeability during the change of gas pressure include the adsorption of coal, change in effective stress, and Klinkenberg effect (ie, the gas slippage effect) under low pressure . When the total stress is constant, the increase in pressure of the pore fluid will reduce the effective stress within the coal body (ie, total stress minus the pore pressure), leading to the expansion of the pores and the opening of the fractures, thereby increasing the permeability.…”

“…On the one hand, CBM is the primary cause of disasters in coal mines, and its presence can lead to disasters such as gas outbursts and explosions . On the other hand, CBM as an efficient and clean energy source has become a promising new resource and has attracted considerable interest from governments, scholars, and entrepreneurs . China's high gas coal seam has the characteristics of complex geological structure, a dense coal matrix, high gas adsorption, and low permeability, which makes gas drainage difficult with low extraction efficiency .…”

Experimental Study on Evolution of Fracture Network and Permeability Characteristics of Bituminous Coal Under Repeated Mining Effect

“…Coal seam groups are frequently mined using the pressure relief method of multiple protective layer mining (Cao et al, 2018). With repeated loading-unloading of coal seam groups, the deformation, crack initiation, and propagation occur in the protected layer (bottom coal seam) and is accompanied by great permeability enhancement (Jiang et al, 2019;Zhang et al, 2018c). Therefore, it is topical to study the law of permeability variation under repeated mining operations in coal seams.…”

Evaluation of Coal Seam Gas Drainability for Outburst-Prone and High-CO2-Containing Coal Seam

“…Under certain conditions, different types of coal exhibit different sorption behavior with various gases [24][25][26][27]. Gas content and gas composition are some of the most important factors that affect coal mine operation and safety and are highly significant in CSG resource assessment and recovery operations [3,22,28,29]. To prevent coal and gas outburst, the outburst threshold limit value (TLV), which stipulates the CSG limit for mining, has to be established for each mine.…”