Characteristics and Physical–Environmental Coupling Evolution Model of Immediate On-Site Gas Desorption from Coal during Postmining Activities

Methane emissions from postmining activities originate from gas dissipation during transport and storage. This study investigates the immediate desorption characteristics and evolution laws of postmining coal through long-term tests on coarse particles and isothermal tests on fine particles under varying parameters. Results show a two-stage desorption process: a rapid linear growth stage posthoisting but before transport and processing, followed by a gradual decline and stabilization. The desorption volume exhibits a two-stage trend with coal rank, fluctuating from low- to high-metamorphic bituminous coal and increasing linearly from high-metamorphic bituminous coal to anthracite. Elevated ambient temperatures and smaller particle sizes significantly accelerate desorption rates. Integrating the Borges and exponential empirical models, a multiparameter coupled mathematical desorption model was constructed incorporating time, vitrinite reflectance, temperature, and particle size. The model shows excellent fitting performance for raw coal from typical mines (R2 > 0.98). This model effectively solves the challenge of accurately estimating initial gas loss during postmining activities. These findings provide a solid theoretical and experimental foundation for the measurement and accounting of postmining methane emissions.