Adsorption characteristics of bituminous coal seams in Zonguldak Basin

Zonguldak Coal Basin, located on the Black Sea coast, is the main part of the Upper Carboniferous bituminous coal basin of Turkey. Much of the bituminous coal mining has thus been concentrated in the Zonguldak Basin. The estimated coal reserve, carried to 1200 m under sea level, is about 1.32x10⁹ tons of coal in this basin. 57 coal seams have been identified and 38 are workable with their thickness varying from 0.7-10 m and dips from 0-90°. The most important coal seams are the Cay and Acilik seams having average thickness of 6 and 4.5 m, respectively. Furthermore, the Sulu, Hacimemis, Domuzcu and Buyuk seams having an average thickness ranging from 1.5 m to 2.5 m are the other coal seams which are regarded as important for coal production. The aim of this study is to determine the gas adsorption characteristics of coal seams in the Zonguldak Basin. A number of samples were collected from 8 different seams. The adsorption characteristics of samples were measured and attempts made to correlate the results with different coal properties determined with the help of proximate analyses. Methane adsorption isotherms were measured at constant temperature of 25°C at different gas pressures up to 50 bar and the results were discussed in relation to the gas capacities of coal seams. Langmuir equation was used to interpret the adsorption isotherms. Results of the interpretation of the adsorption isotherms indicate that Langmuir (monolayer) adsorption capacity of coal seams varies between 10.3 m³/t and 18.2 m³/t. Although the respective data are highly scattered, a certain correlation could be defined between different coal properties and the adsorption capacity. The most apparent correlation is observed between the ash content and the gas adsorption capacity. The trends between Langmuir adsorption capacity and ash content are generally in accordance with the trends observed in other coal basins.