Simulation of biogenic coalbed gas from anthracite in the south of Qinshui Basin, China

Abstract

High-rank coal, such as anthracite, has been considered difficult to generate biogas because of the high coalification degree. Selecting anthracite from Sihe Coal Mine, Qinshui Basin, China, as substrate, this study carried out a simulation experiment of biogas generation for 80 days, the purpose of which was to verify whether anthracite could be biodegraded to produce biogas under laboratory conditions. The results showed that the selected anthracite can be utilized by methanogenic bacteria to produce biogas and the approximate production field was 1.79 mL/g, which was less than that of the lower rank coal of other published studies. The generation process can be divided into a rapid growth stage (0–30 days) and a slow descent stage (30–80 days). CO2 and CH4 are the main components of biogas, although some heavy hydrocarbons were also tested. The CO2 concentrations were low (< 30%), and the δ13C-CH4 values were positive (−39.9‰ to −45.8‰), which suggested that the main biogas generation pathway was acetic fermentation. But at the same time, the concentrations of CH4 and CO2 were mutually increasing and decreasing with the passage of experiment time, and δ13C-CH4 tends to be lighten in the later stage(40–80 days), suggesting that parts of biogenic CH4 were generated by way of CO2 reduction.