Impact of Coal Particle Size and Rank on Methane Adsorption and Coal and Gas Outburst Risk: An Experimental Investigation

Abstract This study investigates the influence of coal particle size on methane adsorption capacity, a critical parameter for optimizing coalbed methane recovery and assessing the risk of coal and gas outbursts. Coal samples were sourced from three Chinese coal mines Qinan (QN), Qingdong (QD), and Chensilou (CSL) representing a range of metamorphic coal ranks. The samples were divided into three particle size ranges (0.074-0.2 mm, 0.2–0.25 mm, and 0.25–0.5 mm), and their methane adsorption characteristics were evaluated using the Langmuir isotherm model. Results indicate a clear trend: smaller particle sizes enhance methane adsorption due to an increased surface area. Additionally, methane adsorption capacity is inversely correlated with coal rank, with CSL (anthracite) samples showing lower adsorption compared to QN (gas coal) and QD (fat coal) at equivalent particle sizes. The study also evaluates the coal and gas outburst risk, revealing that coal seams with higher methane adsorption and specific pore structures are more prone to outbursts under critical pressure conditions. These findings contribute to the development of more effective strategies for coalbed methane extraction and highlight critical safety considerations for mitigating coal and gas outbursts in mining operations.