准东煤热解动力学单一扫描速率法应用局限性

为提高单一扫描速率法在煤热解领域的实际应用有效性,以3种不同升温速率下准东原煤样品的热解失重数据为研究对象,应用单一扫描速率法进行动力学计算,分析分段观点和失水脱气阶段失重对计算结果的影响,探讨能否得到准确且唯一的动力学3因子以及动力学3因子是否具有明确的理论意义等几个问题.结果表明:在分段方面的不同观点对高匹配度模式函数的类别及Arrhenius参数均具有显著影响,连续转化率观点下得到的表观活化能E明显低于独立转化率观点下的;当采用连续转化率观点时,排除失水脱气阶段的失重不仅影响其他阶段的区间划分,还将使E值降低;结合积分和微分法,在3个不同升温速率下分别匹配这两种方法,也不能获得准确且唯一的动力学3因子,因此动力学3因子的理论意义是有限的;失重数据的预处理方法和模式函数的选择,对于动力学参数的评价和交流是十分必要的,以动力学3因子解释热解机理时要十分谨慎.

Application limitations of single scanning rate method in pyrolysis kinetics of Zhundong coal

To improve the application effectiveness of single scanning rate method in the coal pyrolysis field, the weight loss data of temperature programmed pyrolysis of Zhundong coal at three heating rates were investigated and the kinetic parameters were calculated using single scanning rate methods. Several problems such as the impacts of segmentation viewpoint and weight loss in the dehydration and degassing stage on the kinetics calculation results, the possibility of obtaining an accurate and unique kinetic triplet and the theoretical significance of kinetic triplet were analyzed. The results show that the selected segmentation viewpoint affects the well-fitted model functions and Arrhenius parameters, the apparent activation energy (E) values based on sequential conversion viewpoint are obviously lower than those based on independent conversion viewpoint. When the sequential conversion viewpoint is used, excluding the weight loss in dehydration and degassing stage affects the intervals of the other stages and reduces the E values. The comprehensive application of the integral and differential methods as well as the three heating rates can not provide an accurate and unique kinetic triplet, so the theoretical significance of kinetic triplet is limited. Clarifying the pretreatment method of weight loss data and model function chosen are quite necessary for the evaluation and communication of kinetic parameters, and the explanations of pyrolysis mechanism using kinetic triplets should be made with extreme care.