Experiment Study on Deformation Characteristics of Gas Adsorption and Desorption of Confined Coal

In order to investigate characteristics of CH₄ adsorption and desorption in anthracite, YKDPump70 CO₂-ECBM experimental equipment was used to carry out coal deformation through injecting CH₄ to coal samples （φ50 mm×100 mm） with constant pressure under 18 MPa bulk stress at 20 ℃. The main results show that: the radial deformation of coal and the axial deformation of coal changed with time is similar during the whole adsorption and desorption process, the amount of adsorption swelling deformation of coal sample is larger than desorption shrinkage deformation of coal sample, there is a certain residual deformation of coal samples. Under different adsorption pressure, desorption amount and axial deformation, radial deformation of coal body increased with time and eventually stabilized, and the variation of them is basically consistent, presenting logarithmic form. During 12 hours of CH₄ desorption, relationship between CH₄ desorption amount q and axial strain, radial strain ε of coal body is linear under 18 MPa confinement pressure, that is ε=aq+b, and a and b are fitting constants.