低甲烷气氛下褐煤的低温氧化特性研究

Study on low temperature oxidation characteristics of lignite in low methane atmosphere

为研究褐煤在低CH_(4)气氛下的低温氧化特性,采用X射线光电子能谱(X-ray Photoelectron Spectroscopy,XPS)试验和热重-差示扫描量热(Thermogravimetric Analysis-Differential Scanning Calorimetry,TG-DSC)试验分析了CH_(4)体积分数为0、1%、2%、3%和4%的煤样的特征参数,从微观和宏观两方面探究了5种不同CH_(4)体积分数对煤氧化的影响。结果表明,在CH_(4)体积分数4%下氧化后煤样中羟基和羧基的含量均高于体积分数为0的条件下,CH_(4)对煤中羟基和羰基向羧基的转化及芳香烃和脂肪烃的反应活性有抑制作用;煤低温氧化活化能随CH_(4)体积分数的增大而增大,放热量呈降低趋势,表明低体积分数CH_(4)抑制煤的低温氧化进程;与O_(2)相比,CH_(4)具有更高的沸点和气体临界温度,煤对CH_(4)的吸附能力大于O_(2),因此在不同CH_(4)体积分数下的低温氧化过程中,CH_(4)会占据正常空气气氛中O_(2)的部分吸附空位,减少煤与氧的物理化学吸附,进而抑制煤自燃的发生。

To study the effect of low CH_(4)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 CH_(4)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 CH_(4)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 CH_(4)volume fraction;the content of hydroxyl and carboxyl groups in the oxidized coal samples under the condition of CH_(4)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.CH_(4)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 CH_(4)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 CH_(4)volume fraction,and the exothermic heat decreases with it.The low CH_(4)atmosphere inhibits the low-temperature oxidation reaction of coal,and CH_(4)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.