Free radical in situ analysis and change of spontaneous combustion characteristics after pre-oxidation for thermal upgraded lignite

doi:10.11949/j.issn.0438-1157.20170532

Abstract

Abstract:

The difference of spontaneous combustion liability of fresh samples (SA) and pre-oxidation samples (SB) of lignite upgraded at different temperature,were tested by the experiment equipment of temperature programming.Free radicals in situ were dynamically analyzed by X-band electron spin resonance spectroscopy (ESR) and the effect of pre-oxidation on spontaneous combustion liability was surveyed.The results showed that the spontaneous combustion liability of SA reduced with rising upgrading temperature.With the storage time extension in natural environment,lignite upgraded at 105-500℃ was effected by pre-oxidation.The spontaneous combustion liability increased in varying degrees,and lignite upgraded at 400℃ became easy to spontaneous combustion as well as raw lignite.During the oxidation process of spontaneous combustion,being different from fresh samples,the free radical concentration for pre-oxidation samples increased with increasing adsorbed oxygen amount.Pre-oxidation not only improved the free radical amount of upgraded lignite,but also made the continuous generation of new free radical and kept the self-heating and temperature rising in the later part of accelerating oxidation phase.But micromolecule free radicals were rapidly consumed and loss 80% for the fresh sample upgraded at 400℃,which made it could not provide new free radicals and maintain oxidation reaction.

Key words: thermal upgrading, lignite, pre-oxidation, characteristics of spontaneous combustion, free radical

摘要：

针对不同温度热提质褐煤新鲜样及其自然环境中储存一定时间后的预氧化样，利用订制的自燃测定实验装置测得各样品的自燃倾向性差异，采用X-band电子自旋共振波谱仪进行自由基动态原位分析，研究预氧化对热提质褐煤自燃特性的影响。结果表明，热提质温度升高，新鲜样的自燃倾向性降低。但随着储存时间延长，105~500℃热提质褐煤发生预氧化，自燃倾向性不同程度地增加，400℃热提质后的预氧化样与原煤一样易自燃。在自燃氧化过程中，与新鲜样不同，预氧化样的吸氧量增加，自由基浓度也增加。预氧化不仅使热提质褐煤自由基增加；且在自燃的加速氧化阶段后期，不断产生自由基，维持氧化自热升温。而400℃热提质褐煤新鲜样在自燃氧化初期消耗大量小分子自由基，损失达80%，因不能持续产生活性自由基难以维持自燃氧化反应进行。

关键词: 热提质, 褐煤, 预氧化, 自燃特性, 自由基

CLC Number:

TQ536

LIU Lihua, CHU Mo, DANG Tongtong, CHANG Zhibing, QU Yang. Free radical in situ analysis and change of spontaneous combustion characteristics after pre-oxidation for thermal upgraded lignite[J]. CIESC Journal, 2017, 68(10): 3967-3977.

刘丽华, 初茉, 党彤彤, 畅志兵, 曲洋. 热提质褐煤预氧化后自燃特性变化及其自由基原位分析[J]. 化工学报, 2017, 68(10): 3967-3977.

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