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Generation and Mechanism of Gas from Brown Coal Under Action of Parent Bacterium

Author: WangAiKuan
Tutor: QinYong
School: China University of Mining and Technology
Course: Geochemistry
Keywords: secondary biogenic coalbed gas brown coal methanogen generation mechanism impact factor
CLC: P618.11
Type: PhD thesis
Year: 2010
Downloads: 190
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Abstract

Elucidating the characteristics and mechanism of the reaction of microorganisms and organic matter in coal to produce bio-gas is a very important foundation to the further understanding of the genesis of coalbed gas and the innovation of coalbed gas exploration. So we select the brown coal in Zhaotong basin as the research object to study the generation of secondary biogenic coalbed gas, and then discuss its generation mechanism.The results show that, the brown coal samples have active anaerobic bacteria, in which cellulose decomposition bacteria are in the majority and sulfate-reducing bacteria are very few. Local methanogen are successfully enrichment cultivated and they are mainly G+ bacillus, and the individual sizes have large differences. Based on that, the local bacteria and brown coal samples are selected as bacterial sources and substrates to study the generation of secondary biogenic gas from the brown coal. The results prove that, after resting period, the local anaerobic bacteria could use the brown coal to produce a large amount of biogenic gas. Secondary biogenic coalbed gas has two generation periods. The substrate that is biodegraded to produce gas in the first period is humic matter, which in the second period is inertinite and liptinite. The amount of methanogen and content of humic matter in the brown coal influences the generation potential of secondary biogenic coalbed gas directly and the mineral in coal has significant effect on the production of the secondary biogenic coalbed gas. The generation path way of CH4 in the first cycle is acetate fermentation and the second with CO2-reduction involved.The results show that, the value of bothδ13C1 andδD of the produced CH4 are in the normal distribution ranges compared with those of biogenic methane. With the time increasesδ13C1 decreases, which is mainly controlled by the substrate style and the generation path way of CH4. 12C significantly transfers from raw coal to biogenic methane and the reason may be the inheriting from original source and the component of organic maceral in coal. Meanwhile, it is found that, by the degradation of anaerobic bacteria, saturated hydrocarbon in the brown coal group is the main biodegraded composition. Anaerobic bacteria degradation ability to even-numbered alkane is stronger than to odd-numbered alkane, to n-alkanes stronger than to isoalkane, to n-alkanes with lower carbon number stronger than to n-alkanes with more carbon number, and only in the later stage of biodegradation the long chain alkanes starts to be degraded by bacteria significantly.Based on the experimental results, the generation of secondary biogenic coalbed gas from brown coal is considered to be the result of interaction of various microorganisms. With the biodegradation, the dominate bacteria and enzyme in the system are changed and replaced, which leads to the changes of pH and concentrations of VFA. In the initial stage of biodegradation, fermentation bacteria is the dominate bacteria and methanogen and activity of coenzyme F420 are inhibited by the acid matter produced by fermentation bacteria. Syntrophic acetogenic bacteria become dominate bacteria followed by fermentation bacteria. They use the metabolites from fermentation bacteria to produce acetate and H, which shows the food chain relationship with fermentation bacteria. Activity of coenzyme F420 increases quickly after resting period and reaches the maximum at the peak of biogas generation, showing the good adaptability of local methanogen to brown coal substrate and activity of coenzyme F420 is the effective index to evaluate the biogas production.Through changing the gas production conditions, the effects of different styles of substrate, brown coal size, mineral drainage and gangue on the generation of secondary biogenic coalbed gas from brown coal are studied. The results show that, different ratios of yeast extract, methanol and odium acetate solution have inhibition or activation effect on the generation of the secondary biogenic coalbed gas. Smaller brown coal size is good for increasing the gas production. The adding of mining drainage with different proportions activates the production of the secondary biogenic coalbed gas effectively. Gangue itself can not be substrate used by anaerobic bacteria.

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