Sorption Characteristic of Coal, Particle Size, Gas Type and Time

Sorption characteristics of Bulli seam coal samples were examined with respect to coal particle size, gas type and time. Sorption tests were carried out by the indirect gravimetric method for determining gas content in coal. Various coal particle sizes were tested in addition to 54 mm diameter coal core. The other coal sizes were ±15 mm (-5/8+0.530 mesh) cubical blocks and coal fragments of ±1.18 mm (-0.256+16 mesh), ±6.70 mm (-5/16+0.256 mesh), and ±8.00 mm (-5/8+5/16 mesh). The samples were maintained in specially designed pressure vessels, at constant temperature of 24 °C and subjected to gas pressures up to maximum of 4000 kPa with incremental increasing steps of 500 kPa. All samples were tested with CH4, and CO2. The first group of ±1.18 mm size coal fragments achieved the highest gas adsorption, and the lowest was 54 mm size. Adsorption of carbon dioxide was typically the highest and that of methane was lowest. Furthermore, the tests also showed that the longer it takes to reach the pressure equilibrium the higher the gas adsorption. This study suggests that the gas content in coal depends strongly on gas type, sorption time, and particle size. Sorption time however, appears to be independent of particle size.