Isothermal adsorption and swelling deformation characteristics of soft coal under different moisture content

In order to study the influence of moisture on the isothermal adsorption and swelling deformation characteristics of coal,taking soft coal as the research object,the synchro testing experiments were carried out to measure the swelling deformation and adsorption of coal in the process of gas adsorption under different moisture content by a Gas Adsorption/Desorption induced Deformation Dynamic Testing Equipment.The influence of moisture on isothermal adsorption characteristics and swelling deformation characteristics of coal was analyzed according to the experiment results,the relationship between swelling deformation and adsorption has also been discussed.The results showed that,the existence of water inhibited the swelling deformation,the water content of coal samples increases from 0% to 3.13%,the limit swelling deformation decreases linearly from 10.185×10-3to 4.262×10-3,with a decrease of 58.15%.With the increase of moisture content,the saturated adsorption decreased first and then increased,and the saturated adsorption reached the minimum value when the moisture content was about 1%.The relationship between the swelling deformation and adsorption is complex,obedient to various laws：When the moisture content is only 0-0.75%,the swelling deformation lagged behind the adsorption to the extreme value because of free gas promotes the swelling deformation of coal,and the swelling deformation and adsorption show a parabola fitting relationship.When the moisture content increased to 1.42%-1.66%,the compression deformation caused by the compression effect of free gas on the coal matrix is offset by the swelling deformation caused by the expansion of micro cracks due to the softening and blocking effects of water.The pressure required for the swelling deformation to reach the extreme value is equivalent to the gas pressure required for the adsorption to reach saturation,and the swelling deformation and adsorption show a linear fitting relationship.When the moisture content further increased to 2.66%-3.13%,the softening and blocking effect of water make the free gas inhibit the coal swelling deformation as a whole.After the swelling deformation reaches the extreme value,the coal samples can continue to absorb gas with the increase of gas pressure,and the swelling deformation and adsorption show an exponential fitting relationship.