Storage of N2, He and CH4 in coal: Study and application in a practical case in the central Asturian coal basin (northern Spain)

The behaviour of different gases (He, N2 and CH4) in coal was analyzed using a device for treating raw coal, designed for taking samples in the mine. This device was subsequently used to transport the samples and inject them with the gases under study. Experiments were conducted under different pressures, and a clear relationship was found between the drop in pressure and the occupation of different storage levels.On analysing the pressure evolution it was found that helium rapidly stabilised due to the characteristics of this gas. As for the other gases, N2 showed a percentage fall much lower than that of CH4.In order to compare the storage capacity of different materials with respect to these gases, experiments were performed with different materials which form the mine's ceiling and walls. It was shown that the fall in pressure is very inferior.A fitting equation relating the evolution of pressure with time is proposed which may be used to define the time needed for the gas to stabilize in the coal. A normalized equation, very similar to that proposed by Langmuir, is likewise obtained to characterize the adsorption and desorption processes.