不同变质程度煤热解过程中的软化熔融特性

Softening and melting characteristics of coal with different degrees of coalification during pyrolysis

由于配合煤在焦炉炭化室内部干馏成焦,无法连续观察煤热解过程的动态变化,也不能实时展现煤在不同温度下的热演化行为。为了揭示不同变质程度炼焦煤热解过程中的软化熔融特性,探讨不同升温速率对煤热解过程中胶质体形态变化的影响,采用热载物台显微镜原位观测五种性质不同的炼焦煤在10℃/min,30℃/min和50℃/min的升温速率下热解过程中的软化熔融特征。结果表明:随着升温速率的增加,煤基体内的解聚和分解反应加剧,不同变质程度炼焦煤热解过程中的胶质体铺展系数升高,各向异性的中间相增多,热解塑性区间向高温区偏移;同时快速热解可提高不(弱)黏结煤的膨胀性和软化熔融性。升温速率为50℃/min时热解过程中的各向异性中间相的变化表明,肥煤热解时形成的各向异性中间相最为丰富,说明随着升温速率的增加,煤分子结构受到的冲击更强,导致单元桥键断裂;煤芳香稠环破裂以及脂肪侧链和含氧官能团也快速裂解,产生大量自由基碎片,有助于形成更多胶质体;在热解过程中形成的各向异性中间相具有丰富的多色性,热稳定性较高,更能保持较为稳定的形态和结构,有助于改善焦炭的热态性能。

It is not possible to continuously observe the dynamic changes in the coal py-rolysis process,nor can it display the thermal evolution behavior of coal at different temperatures in real-time due to the dry distillation of coal in the carbonization chamber of a coke oven.To ex-plore the softening and melting characteristics of coking coals with different degrees of coalifica-tion during pyrolysis,an in situ high-temperature heating stage paired with an optical microscope was used to observe the softening and melting behaviors.In this study,the morphological chan-ges in the plastic layer of five types of coking coal were examined at different heating rates of 10℃/min,30℃/min and 50℃/min.The experimental results show that within the coal ma-trix,depolymerization and decomposition reactions intensify,and the spreading coefficient of the plastic layer for coal with different degrees of coalification during pyrolysis increases with the heating rate.Concurrently,the number of anisotropic intermediate phases increases,and the range of pyrolysis plasticity shifts towards the high-temperature zone.This process can improve the expansion and softening melting properties of non(weak)bound coal through rapid pyroly-sis.The most abundant anisotropic intermediate phase forms during the pyrolysis of fat coal at a heating rate of 50℃/min.This indicates that the impact on the coal molecular structure intensi-fies with increasing heating rates,leading to the fracture of unit bridge bonds,the rupture of coal aromatic rings.The rapid cracking of fat side chains and oxygen-containing functional groups produces a large number of free radical fragments,which facilitate the formation of more plastic layers.The anisotropic intermediate phase formed during the pyrolysis process exhibits rich poly-chromism,high thermal stability,and is able to maintain a more stable morphology and struc-ture,which contributes significantly to enhancing the thermal performance of coke.