煤低氧自燃及其残余物复燃特征试验研究

Experimental study on the characteristics of coal spontaneous combustion under oxygen-depleted atmosphere and re-ignition of its residues

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16173.73 J/%降至12647.56 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。

To investigate the processes of coal spontaneous combustion under oxygen-depleted atmosphere and re-ignition of its residues,the coal samples were oxidized at 200℃,300℃,and 400℃under 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 analysis 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 16173.73 J/%to 12647.56 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 decreases 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 oxidation 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 corresponding to the maximum mass first decreases and then increases,while both the ignition point temperature 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 changes 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.