Low Rank Bituminous Coal With/without CO₂ Injection Simulation Of Biogas Production And Characteristics And Its Pore Structure Changes

Based on the simulation of biological gas production of low rank bituminous coal with/without CO₂ injection,SEM and low temperature liquid nitrogen experiment,the characteristics of the concentration of gaseous components,methane production,anion concentration of produced water,microflora structure,surface morphology and pore size structure of coal samples during the gas production process were analyzed,and the effect of CO₂ injection on microbial degradation of low rank bituminous coal gas production was expounded.The evolution characteristics of the community structure of archaea and bacteria in the process of microbial degradation and gas production,as well as the effects of CO₂ injection on environmental factors and methanogens,were analyzed,and the interaction characteristics of the system composed of CO₂-H₂O,microbe and coal were revealed.The results show that:1)The biodegradation of low-rank bituminous coal is mainly composed of CH₄ and CO₂,with a small amount of H₂;2)Acetic acid fermentation is the main way to produce gas,while CO₂ injection makes CO₂ reduction pathway exist in the gas production pathway,H₂ injection promotes and strengthens the CO₂ reduction pathway to a certain extent.3)The pressure in the fermentation flask with or without CO₂ increased first and then decreased,reaching the peak gas production pressure in about 30 days.4)The cumulative production of CH₄ in fermentation bottles injected with CO₂ was higher than that without CO₂ injection in the first 30 days,and the cumulative production of CH₄ in fermentation bottles from 30to 96 days showed a"stagflation"slow rise,with the highest production reaching6cm³/g.CO₂ injection could change the medium environmental conditions of microbial methanogeneration.5)During microbial degradation and gas production,the number of bacterial Operational Taxonomic units（OTUs）increased while that of archaea decreased.6)The greater the amount of CO₂ injected,the greater the influence on the growth of bacterial community;7)The number of OTUs in 500ml fermentation system was higher than that in 250ml fermentation system,and the larger fermentation system was more conducive to the growth and metabolism of archaea;8)The changes of cationic concentration in the fermentation system were directly related to the growth and metabolism of microorganisms.Cationic concentration was weakly correlated with archaea,but strongly correlated with bacteria.9)Methane metabolism is mainly H₂/CO₂reduction and methyl-nutrition pathway;10)After CO₂ injection,the surface of most coal samples becomes rough,with an increase in attached debris particles,corrosion pores,and crack opening.However,the degree of pore structure modification in the CO₂ injection experimental group is smaller than that in the non CO₂ injection control group,indicating that CO₂ injection has overall suppressed the modification effect on the coal pore size structure.