Control Mechanism Of Coal Macerals On Biogenic Coalbed Methane Production

Various factors are influential to the process of microbial methane generation from coal used as metabolic substrates.Aiming to investigate the control effect of coal macerals on biogenic coalbed methane(CBM)production,the current study focused on firstly the separation and enrichment of each maceral groups from coal materials obtained respectively from Qianqiu mine,Yima,Quanling mine,Datong,Malan mine,Shanxi and Shaqu mine,Liulin,using bare-hand plus float-sink methods.Then,indigenous microbial populations extracted and cultured from mine water were further applied to the simulation experiments for microbial methane production,in which each of the three separated maceral groups were subjected to the microbial decomposition individually.By means of elemental analysis,Fourier transform infrared spectroscopy(FTIR)and low-temperature liquid nitrogen(LTLN)tests were the characterization of each coal macerals achieved,and then several key parameters including biogas yield,C/H ratio,chemical structure and pore-fracture characteristics for different coal macerals were thoroughly discussed.The results show: a.The inertinite exhibits a highest enrichment rate among the three maceral groups for various sources of coal materials,especially for those obtained from Yima and Datong.b.The variations of parameters including total gas yield,CH4 production and concentration,before-and-after changes of pH values in reactors and mass consumption rate,etc have been met significantly with vitrinite,successively followed by raw coal in the middle and inertinite as the least.c.The H/C ratio varies consistently with the effect of gas generation,which is convinced by the result that vitrinite-rich coal materials with a highest H/C ratio are of great potential for biogenic methane generation.d.The high contents of aliphatic hydrocarbon and element hydrogen,low proportions of aromatic hydrocarbon and poor degree of aromatization are the advantageous conditions for higher production of biogenic methane from the coal materials with similar rank.e.Except for the relatively lower percentages of micropores,the openness and connectivity of pores in vitrinite-rich coals are better than that of raw and inertinite-rich coal materials,which is likely to explain the result that a higher methane production has been met with using vitrinite-rich coals as substrate.It has also been found that the methane production effect has little relevance with average pore diameter and specific surface area.The present study will not only serve as a theoretical reference for the future laboratory experiments and pilot field application of biogenic methane production from different coal macerals,but broaden the research areas of bogenic CBM engineering and speed up the domestic industrial development of CBM in China.