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煤自热低温阶段“自限制”特征的理论与试验研究

Theoretical and experimental study on low temperaturestage of coal self-heating

  • 摘要: 为深入分析煤自燃特性,以有效减少煤矿内因火灾,根据气固反应动力学相关理论,提出外部环境允许条件下煤氧反应低温阶段温度也并非始终“加速上升”,在一定时期会内出现“自限制”特征,基于此,对颗粒煤低温绝热条件下的反应步骤进行分析,推导出考虑界面效应的煤低温绝热氧化升温理论模型,然后根据4个不同变质煤样的绝热氧化试验结果进行论证。结果表明:煤颗粒的绝热氧化反应前期,温度随时间不断增长且升温速率随试验的进行而加快,呈类指数分布特征,但后期中低变质煤升温速率随试验进行开始逐渐减慢,服从半抛物线趋势变化;随着变质程度的提高,煤低温绝热氧化反应“自限制”温度有向高温方向偏移的趋势,极大升温速率逐渐降低;低温绝热氧化升温过程可分为物理吸氧放热升温阶段、自由加速升温阶段、受限减速升温阶段和全面反应阶段,其中受限减速升温阶段主要是由于“氧化层”界面作用产生,实际自燃状态分析中应注意该效应的影响。

     

    Abstract: Understanding of coal spontaneous combustion could help reduce fire disaster in coal mines.This paper proposes a new view that temperature of coal-oxygen reaction in the low temperature phase of coal spontaneous combustion is not always accelerated increasing, even if external environment allows, but has the “self-limiting” feature in a certain period of time.The paper analyzes the reaction steps and coal oxidation model under low temperature adiabatic conditions and develop a theoretical model.The model is then validated by conducting adiabatic oxidation experimental on four different coal samples.The results show that at the beginning of adiabatic reaction between coal particles and oxygen, coal temperature accelerated increases with time, showing an exponential correlation.Then, the heating rate of low metamorphic coal samples decreases with time, showing a semi-parabolic correlation.With the increase of coal metamorphic degree, restricted temperature of low temperature adiabatic oxidation has the trend of shifting to high temperature and extreme heating rate decreases gradually.Adiabatic oxidation of coal at low temperature includes four stages, namely physical oxygen adsorption heating stage, free acceleration heating stage, restricted decelerated heating stage, and full reaction heating stage.The restricted decelerated heating stage is mainly resulted from interface effect of thin oxide layer.This effect should be paid attention to in the actual analysis of coal self-ignition.

     

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