Study on difference of biogas production in different rank coal

In order to investigate the difference of biogas production from different rank coal samples, long flame coal, coking coal and lean coal were chosen to analyze the biogas production characteristics, organic matter composition, coal surface structure and characteristics of microbial adsorption by the determination of the biomethane production and GC-MS(Gas chromatograph- mass spectrometer), scanning electron microscope tests. The results showed that the higher the coal rank is, the lower the cumulative biogas production is, and the biogas production of low rank coals was significantly higher than that of high rank coals. For the results of GC-MS tests, VFA(Volatile Fatty Acid) and methyl compounds were produced in the 10th day of biogas generation process, while the VFA and other small molecular substances were not detected in the 15th day of the long flame coal experimental group and coking coal experimental group, new macromolecular substances were generated. However, VFA was still detected in the lean coal experimental group, this may be attributed to the decrease of methanogens activity in the late stage of fermentation. At the same time, the content of high fatty acid is one of the reasons for inhibiting methane generation. Aromatic hydrocarbons are more suitable for microbial degradation than aliphatic hydrocarbons, so its proportion in liquid products is also the main factor for affecting the final methane production. At the same time, it is different from the cell morphology of coal surface, and the cell density increased in the peak period of biogas production from three coal samples. The surface of the long flame coal was uneven, and the surface roughness increased gradually. There is no obvious change in the surface structure of coking coal and lean coal. The above results showed that low rank coal was more suitable as carbon source for methanogens. The VFA, fatty acid and aromatic hydrocarbons contents in the fermentation solution can indirectly reflect the intensity for the conversion of coal to biogas, it can also indirectly characterize the adsorption characteristics of bacteria on coal surface. There is a positive relationship between the cell density of bacterial community on the surface of coal samples and biogas production, which provides reference for the coal liquefaction and clean utilization of coal.