Experimental study on the effect of moisture on low-rank coal adsorption characteristics

• The effect of moisture on adsorption characteristics of low-rank coals was studied.
• A new device was developed to prepare coal samples with different moisture contents.
• The influence of moisture on low-rank coal bed methane development was discussed.

To study the effect of moisture on the adsorption characteristics of low-rank coals, samples from the Shenbei and Tiefa coalfields in China were examined. Here, a new water injection and gas adsorption device was developed to prepare the coal samples with a variety of moisture contents, and the isothermal adsorption characteristics of the coal samples for methane were tested. The results indicate that the methane adsorption isotherms of low-rank coals are consistent with the Langmuir adsorption law. Moisture clearly inhibits the adsorption ability of low-rank coals for gas and the degree of inhibition increases with increasing moisture content. However, the growing amplitude of the inhibitory effect decreases gradually as the moisture content increases. The exponential formula can properly fit the data of the gas adsorption capacity of low-rank coals with changing moisture content, and the fitting parameters y0, A and c show the change in the gas adsorption law at the different gas pressures. Meanwhile, these fitting parameters have an exponential relationship with gas pressure. Furthermore, the Langmuir pressure of the experimental coal samples decreases with increasing moisture content. On this basis, the influence of moisture on low-rank coal bed methane (CBM) development is discussed in this paper.