Abstract
Methane(CH4)and carbon dioxide(CO2)are primary components of coal seam gas(CSG).Understanding their adsorption-desorption hysteresis characteristics,along with the fundamental mechanism,is crucial for CSG exploitation and related hazards mitigation.This research focused on the representative Bulli coal seam in the Sydney Basin,Australia.Through the purpose-built indirect gravimetric high-pressure isothermal adsorption-desorption hysteresis experiment,a novel Langmuir-based desorption model,incorporating hysteresis effect and residual gas,was proposed.Quantitative characterization of the adsorption-desorption hysteresis degrees of CO2 and CH4 in coal particles of various sizes and in Φ50 mm × 100 mm intact coal samples were achieved using the improved hysteresis index(IHI).The exper-imental findings validated that the proposed desorption model accurately describes the desorption behavior of CO2 and CH4 in coal(R2＞0.99).Based on the adsorption-desorption properties of ink-bottle-shaped micropores and pore deformation caused by gas adsorption-induced coal expansion,the occurrence mechanism of adsorption-desorption hysteresis and the fundamental reasons for the pres-ence of residual gas were elucidated.Furthermore,the study explored the impact of CO2 and CH4 adsorption-desorption hysteresis effects on coal and gas outbursts,suggesting that coal seams rich in CO2 do not have a higher propensity for outbursts than those rich in CH4.
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