Accelerating methane desorption in lump anthracite modified by electrochemical treatment

• The desorption rate of methane from anthracite after electrochemical modification increased by 68%.
• The methane desorption time constant for lump anthracite changed according to negative exponential rules.
• The mineral-filled fractures of coal samples were unblocked by electrolytic reactions.
• Electrophoresis and electro-osmosis caused charged particles and the electrolyte in the coal matrix and cleats to move.

The slow rate of methane desorption in coal can seriously affect the effectiveness of coalbed methane production. An electrochemical method was proposed to modify coal and accelerate methane desorption. The desorption kinetics of methane from lump anthracite, before and after modification, were studied at four adsorption equilibrium pressures using our own manufactured devices, electrochemical modification equipment and lump coal adsorption–desorption apparatus. Based on mercury intrusion tests and SEM-EDS analyses, the possible modification process of accelerating methane desorption in lump anthracite was further analyzed. The results showed that (1) the average desorption rate of methane from anthracite after modification, at the low end of the pressure ranges from 1 to 4 MPa, increased by 68% over the period of reaching desorption equilibration; (2) with increasing adsorption equilibrium pressure, the methane desorption time constant for lump anthracite changed according to negative exponential rules; and (3) in the anodic zone, the mineral-filled fractures of coal samples were unblocked by electrolytic reactions. In the cathodic zone, electrophoresis and electro-osmosis caused charged particles (clay minerals and coal particles) and the electrolyte in the coal matrix and cleats to move, which led to the initiation, development and connection of pores or fractures. These changes increased the number of Darcy flow channels and shortened gas diffusion distance and desorption time.