Generation And Adsorption Mechanism Of Coal Spontaneous Combustion Index Gases And Goaf Dangerous Zones Classification Division

The fire-fighting is one of the important tasks of coal mine safety,and the index gases monitoring is often used for judging the oxidation state of goaf.However,the existing studies of the microscopic generation and adsorption mechanism of index gases have not been effectively applied during macroscopic production.To solve this problem,the dissertation combined molecular dynamics simulation,the adsorption simulation and heating experiment of coal samples,to explore the relationship between generation and adsorption of index gases,and combined with the oxygen concentration distribution in goaf,build a kind of spontaneous combustion danger zone division method based on the index gases and oxygen concentration distribution,which provides the possibility for scientific prevention of spontaneous combustion in goaf.According to different coal quality and different spontaneous combustion tendency,coal samples from Yangmei No.5 Mine,Dongrong No.2 Mine,Hongqingliang Mine,Gaojialiang Mine and Hongmiao Mine were selected for industrial analysis,element analysis,FTIR,XPS and ¹³C-NMR.According to calculation and analysis of the test results,the C/H/N/O/S element ratio of coal molecules,the connection of fat structure,oxygen-containing functional group,aromatic and other naphthenic structure,the main forms of sulfur or nitrogen functional group,and the general structure of carbon skeleton of coal molecules were obtained.The structural models of coal molecules in each mine are established respectively.The Reax FF molecular dynamics simulation of coal molecules were carried out,and the formation rules of C2H2/C2H4/CO/CO2 were obtained.The peak production of C2H2 and C2H4occurs in the lean oxygen state,and the value is mainly affected by the number of fatty chains.Therefore,the peak production is inversely proportional to the coal rank,with the exception of Dongrong No.2 Mine.The reason is that although the coal sample of Dongrong No.2 Mine is bituminous,the number of fatty chains is relatively high.The peak production of CO and CO2appears in the rich oxygen state,and the peak production is mainly related to the carbon atoms content of coal molecules.Therefore,there is little difference in the coal molecules with similar carbon atom content.The molecular dynamics simulation results of each index gas was analyzed,and the reaction path of each index gas was obtained.The heating experiment of each coal sample was carried out,and the peak concentration order of C2H2 and C2H4 of each coal sample was basically consistent with that of Reax FF simulation by Logistic fitting,which verified the reliability of the simulation.The peak concentrations of CO and CO2 are limited by the carbon atom content of models and the difficulty of spontaneous combustion in different rank coal experimental samples,so the performance is different in the simulation and experiment.The peak concentration of each coal sample,as the highest concentration of oxidation spontaneous combustion point in goaf,is applied to the interpretation and example of classification method of spontaneous combustion dangerous zone in goaf.The adsorption capacity of each coal molecule to index gases was simulated,and the influencing factors of the adsorption capacity and the characteristics of adsorption sites were analyzed.It is found that CO2 has the strongest adsorption capacity and can be adsorbed at the unique adsorption sites of other index gases.The adsorption of coal molecules in Yangmei No.5Mine and Dongrong No.2 Mine shows obvious regularity,and the adsorption capacity from small to large is C2H2<C2H4<CO<CO2.There are some differences in the amount of gas adsorption in other coal samples because of low ranks,but CO2 is the most.In summary,the concept of production-absorption ratio is put forward,which can be used to judge whether the gas is suitable to be used as an index gas in a coal mine.It can be learned that the production-absorption ratios of C2H4 in Yangmei No.5 Coal Mine and Gaojialiang Mine are less than 1,which is not suitable to be used as an index gas in these two mines.The result has also been verified in the construction of the classification method of spontaneous combustion dangerous zone in goaf.The distribution of oxidation zone of each mine is established by FLUENT simulation.By analyzing the molecular dynamics simulation results of index gases,the experimental results of heating experiment and the adsorption law of index gases in low pressure area,the model of index gases generation and adsorption in goaf is constructed.Taking five coal mines as an example,the construction method of spontaneous combustion dangerous zone in goaf is explained,which plays a positive role in scientifically guiding coal mine fire-fighting work.There are 48 pictures,40 tables and 203 references in the dissertation.