Study On The Simulation And Mechanism Of H₂S Biogenesis And Thermogenesis In Coal

With the continuous mining of sulfur-bearing coal seams,abnormal gush of hydrogen sulfide（H₂S）has occurred in coal mines in several provinces in China,and the number of accidents caused by abnormal enrichment of H₂S gas in coal mines has been increasing.However,because H₂S gas is not as common as methane,the depth and breadth of research on H₂S in coal mines by scholars at home and abroad is far less than that of methane,and little research has been done on its formation mechanism,distribution rules,and enrichment factors,etc.The existing results have not yet fully revealed the mechanism of hydrogen sulfide generation in coal mines,resulting in abnormal outflows of H₂S gas in coal mines,which is still a major problem plaguing coal mine safety production at home and abroad.In this study,biological genesis simulation experiments of H₂S production from coal degradation by sulfate-reducing bacteria and thermal genesis simulation experiments of H₂S production from coal reduction by sulfate at higher temperatures were conducted with coals of different degrees of deterioration as research objects,and the following insights were obtained from the two main genesis types of H₂S in coal mines.（1）A strain of sulfate-reducing bacteria（SRB-I）was isolated and identified from typical mine water with abnormal hydrogen sulfide endowment,and the H₂S release pattern and other related parameters of each coal sample during degradation under different conditions were investigated.The results show that SRB-I has the strongest degradation ability for low-rank coal,and high-rank coal is difficult to be utilized.Under the single-factor conditions,the optimal temperature for SRB-I to degrade coal was 30℃,the optimal initial p H was 7.5,and the optimal salinity was 2g/L.The p H value in the system showed an increasing and then decreasing trend during the degradation process,and the redox potential showed a decreasing trend.（2）The raw coal and residual coal before and after degradation were analyzed by industrial and elemental analysis,XPS and XRD.The ash and volatile content in the coal decreased after degradation,and the functional groups were changed,the content of C,H,N and S elements decreased to different degrees,and the content of O elements increased.The XRD diffraction peaks of calcium sulfate,potassium bisulfate and silicon disulfide weakened.The elemental forms of C,N,O and S in the high rank coals before and after degradation did not change much,while the aromatic structure and alkyl side chains of the middle and low rank coals were destroyed,resulting in obvious changes in the elemental forms of C and O,in which the proportion of C-C decreased and the proportion of C=O and OH-increased.the elemental forms of N mainly changed between pyridine nitrogen and pyrrole nitrogen,and the elemental forms of S showed a decrease in the proportion of thiol thiophenol type sulfur and thiophene type sulfur.（3）The product changes of each coal sample during pyrolysis and sulfate thermochemical reduction（TSR）reactions under different conditions were investigated by thermal evolution simulation experiments on coals with different degrees of metamorphism and sulfate.The results show that the initial precipitation temperature of H₂S increases with the coal rank during pyrolysis,and the magnitude of H₂S yield is positively correlated with the sulfur content of the coal.TSR reaction is the main source of thermogenic H₂S,and the H₂S yield can be more than 10 times that of the pyrolysis process.The lower the degree of metamorphism,the more violent the TSR reaction process.Heavy hydrocarbons are preferentially involved in the TSR reaction than CH₄,and CO₂is the signature product of the TSR reaction.（4）The type of sulfate has a greater influence on the TSR reaction.The smaller the radius of the metal cation and the higher the number of charges,the stronger the induction effect and the more likely to trigger the TSR reaction.A moderate increase of salinity can promote the formation of contact ion pairs and thus the TSR reaction,but too high salinity will reduce the solubility of hydrocarbons,especially heavy hydrocarbons,and play an inhibitory role in the TSR reaction.The variation of coal particle size affects the heat transfer process of coal particles and the escape resistance of gas products,thus affecting the degree of reaction,and the smaller the particle size,the more favorable the TSR reaction.（5）The number of molecules in the pyrolysis of coal macromolecules tends to increase rapidly and then decreases slowly.H radicals are present in large numbers throughout the pyrolysis process and have an important influence on the formation of H₂S.H radicals can react with other radicals to form aromatic hydrocarbons or small molecules to facilitate the TSR reaction,and can combine with sulfhydryl groups to form hydrogen sulfide.The number of H₂molecules fluctuates due to the dehydrogenation and hydrogenation reactions during the process.S atoms first migrate to the coke fractions,then to the heavy tars,then to the light tars or sulfur-containing organic gases with the cracking of the heavy tars,and finally to the sulfhydryl groups and H radicals to form H₂S.Theoretical analysis investigated the biogenesis mechanism and thermal genesis mechanism of hydrogen sulfide in coal:three types of biogenesis of H₂S in coal were proposed,namely,sulfate-reducing bacteria can produce hydrogen sulfide by using organic matter in coal,minerals in coal and adsorbed gas in coal,respectively,and the action process and H₂S generation mechanism of the three types were analyzed;two different stages of H₂S generation in the TSR reaction process were proposed and the mechanism of H₂S generation within the different stages was analyzed.In-depth research on the characteristics and laws of hydrogen sulfide production under the degradation and thermal evolution of sulfate-reducing bacteria in coals with different degrees of metamorphosis under different conditions deepens and improves the biological and thermal mechanisms of hydrogen sulfide in coal,which is a guide to enrich and improve the formation mechanism of hydrogen sulfide in coal and the prevention of hydrogen sulfide disasters in coal mines.The dissertation includes 115 figures,56 tables and 237 references.