Methane sorption on bituminous coal - experiments on cuboid-shaped samples cut from primal coal lumps

The paper reports the results of laboratory experiments concerning the accumulation of methane on two coals of different ranks, low- and medium-, (respectively coal type 32.2 and 34.2 by PN-82/G-97002). The tests were conducted on cuboid-shaped solid coal samples (20 x 20 x 40 mm) cut out of pieces of primal coals with a long axis parallel to the bedding plane and by applying the volumetric method. The changes of external dimensions which occurred during CH4 accumulation (sorption induced strains) and the volume of up-taken gas were measured simultaneously. For every coal-gas system, two kinetics of gas accumulation were determined by applying the pressure progression method, as well as adequate kinetics of CH4 induced strains parallel and perpendicular to the bedding plane. Volumetric strain kinetics were calculated. The additional recovery of methane beside normal exploitation of coal seams pose as one of the possibilities of efficient management and use of both of those energy resources. On the other hand high concentration of methane in coal suggests the possibility of emerging of gas and coal outburst. Therefore the designation of correlations between sorption and induced swelling/shrinkage processes on coal and the understanding of the mechanisms that are the basis of these dependences are some of the most important aspects of ECBM recovery and mining operational safety. The presented study has demonstrated that in case of hard coals, the rank and the petrographic composition are two of the key factors that influence the course of sorption processes and the methane induced swelling/shrinkage of coals. The above conclusion was based on the strong differences in courses of acquired strain and gas capacity kinetic curves.