Study on low temperature oxidation characteristics of lignite in low methane atmosphere
To study the effect of low CH4 concentration on the low-temperature oxidation process of lignite,the qualitative and quantitative compositions of elements and different chemical bonds in the oxidized coal samples at five different CH4 volume fraction(0,1％,2％,3％,4％)were obtained by fitting the functional group fractional peaks with an X-ray photoelectron spectrometer,and the mass and heat changes during the low-temperature oxidation of the coal samples at the five concentrations were obtained by a simultaneous thermal analyzer.The effects of different concentrations of CH4 on the oxidation of coal were compared and analyzed from both microscopic and macroscopic aspects.The results show that the C1 content and total elemental content of the coal samples after oxidation are lower than those of the original coal,while the decreasing trend of C1 and total elemental content slow down with the increase of CH4 volume fraction;the content of hydroxyl and carboxyl groups in the oxidized coal samples under the condition of CH4 volume fraction of 4％is higher than those of the other four concentrations,while the changes of aromatic hydrocarbons,aliphatic hydrocarbons and carbonyl groups are opposite.CH4 inhibits the conversion of hydroxyl and carbonyl groups to carboxyl groups in the coal samples.The reactivity of aromatic and aliphatic hydrocarbons is inhibited;the mass loss of coal samples decreases with the increase of CH4 volume fraction,and the characteristic temperature point moves to the high temperature region;the activation energy of coal oxidation at low temperature increases with the increase of CH4 volume fraction,and the exothermic heat decreases with it.The low CH4 atmosphere inhibits the low-temperature oxidation reaction of coal,and CH4 occupies the adsorption vacancies on the coal surface during low-temperature oxidation,which reduces the physical and chemical adsorption of coal with oxygen,and then inhibits the occurrence of coal spontaneous combustion.
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