摘要
为研究煤的低氧自燃及其残余物的复燃过程,在氧浓度5%的条件下,分别在200,300,400℃对煤样进行恒温氧化,采用同步热分析法,测试了原煤低氧自燃及残余物复燃过程中的质量及放热量变化规律,并进一步分析其动力学特征.结果表明:相对于21%氧浓度,在5%的低氧环境中,煤的自燃进程受到抑制,特征温度均升高,最大反应速率由 5.05%/min 降至3.12%/min,降低了38.22%,净放热量由16 173.73 J/%降至12 647.56 J/%,降低了21.80%;动力学模式由随机成核和随后生长转变为相边界反应,与21%氧浓度相比,5%氧浓度的煤表观活化能由91.29 kJ/mol降至81.99 kJ/mol,降低了10.19%;相对于原煤,5%的低氧高温残余物的吸氧增重过程明显受到抑制,残余物对的吸氧增重量随氧化温度的升高而降低,当经历400℃氧化后,残余物复燃的吸氧增重量相对于原煤降低了65.99%;随着氧化温度的升高,质量最大值对应的温度先降低后增大,而燃点温度和燃尽温度降低;放热量均降低,且热分解过程中放热速率的加速趋势逐渐消失;动力学模式由随机成核和随后生长先转变为反应级数,再转变为相边界反应,表观活化能先由81.99 kJ/mol增大至117.67 kJ/mol后减小至117.77 kJ/mol.研究结果对煤自燃隐患的科学治理具有指导意义.
Abstract
To investigate the processes of coal spontaneous combustion under oxygen-depleted atmos-phere and re-ignition of its residues,the coal samples were oxidized at 200℃,300℃,and 400℃un-der the condition of an oxygen concentration of 5%.The variations of mass and quantity of heat release during spontaneous combustion of raw coal and residues were tested based on synchronous thermal a-nalysis method.Furthermore,the kinetic characteristics was analyzed.The results show that:Compared with 21%oxygen concentration,in the 5%low oxygen environment,the spontaneous combustion process of coal is inhibited,and the characteristic temperature is increased.The maximum reaction rate is reduced from 5.05%/min to 3.12%/min,which is decreased by 38.22%,and the net heat release is reduced from 16 173.73 J/%to 12 647.56 J/%,which is decreased by 21.80%.The dynamic mode shifts from random nucleation and subsequent growth to phase boundary reactions.Compared with 21%oxygen concentration,the apparent activation energy of coal with 5%oxygen concentration de-creases from 91.29 kJ/mol to 81.99 kJ/mol,with a decrease of 10.19%.Compared to raw coal,the oxygen absorption and weight gain process of 5%low oxygen high temperature residue is significantly inhibited.The oxygen absorption and weight gain of residue pairs decrease with the increase of oxida-tion temperature.After undergoing 400℃oxidation,the oxygen absorption and weight gain of residue re-ignition is reduced by 65.99%.With the increase of oxidized temperature,the temperature corre-sponding to the maximum mass first decreases and then increases,while both the ignition point temper-ature and burnout temperature decrease.Meanwhile,the heat release decreases,and the accelerating trend of heat release rate during thermal decomposition gradually disappears.The dynamic mode chan-ges from random nucleation and subsequent growth to a reaction order,and then to a phase boundary reaction.The apparent activation energy first increases from 81.99 kJ/mol to 117.67 kJ/mol and then decreases to 117.77 kJ/mol.These findings provide guiding significance for the scientific management of coal spontaneous combustion hazards.
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