ReaxFF方法模拟褐煤热解中氮转化过程

发布时间：2018-05-20 23:39

本文选题：褐煤 + 热解机理　；参考：《华北理工大学》2017年硕士论文

【摘要】：煤无定型的非均相结构导致其热解过程十分复杂。它不但包含众多基元反应,而且产生的中间体寿命极短,无法用实验方法逐一探测。采用基于活性反应力场下的(Reax FF force field,Reax FF)分子动力学模拟方法是实验方法的有效补充,模拟褐煤不同环境下的热反应过程,对含氮自由基的变化进行监测或捕获。通过对其中发生的含氮基元反应统计和归类,探讨褐煤的氮转化机理。以Wolfrum褐煤分子模型作为褐煤体系的结构单元,分别构建了三个热解体系:加氧热解体系(气化过程)、加氢热解体系(液化过程)和热解体系(热解过程)。用LAMMPS程序进行Reax FF模拟计算,并编写相应的了C++程序对模拟计算后的结果进行处理,统计常见的含氮气体产物的分布和模拟过程中发生的含氮基元反应。模拟结果与实验结果基本一致,例如褐煤热解体系和加氢体系中氮氧化物很少,含氮产物以HCN、NH3和腈类物质为主;加氧热解体系中有大量氮氧化物生成,氮氧化物主要为NO。结果表明,热解过程中会生成CH2NH分子、NH自由基、CON自由基和CN自由基等中间体,在加氢热解体系中与氢相互作用可生成HCN、NH3,在加氧热解体系中与氧化剂相互作用可生成NO。该研究为褐煤气化和液化过程中氮转化机理研究提供了可靠的理论依据。
[Abstract]:The process of pyrolysis is very complicated due to the amorphous heterogeneous structure of coal. It not only contains many elementary reactions, but also produces intermediates with very short lifetime, which can not be detected one by experimental method. The molecular dynamics simulation method based on the reactive force field is an effective supplement to the experimental method, which simulates the thermal reaction process of lignite in different environments and monitors or captures the changes of nitrogen-containing free radicals. The nitrogen conversion mechanism of lignite was discussed by statistics and classification of nitrogen-containing elementary reactions. Using Wolfrum lignite molecular model as the structural unit of lignite system, three pyrolysis systems were constructed: oxygen-added pyrolysis system (gasification process), hydropyrolysis system (liquefaction process) and pyrolysis system (pyrolysis process). The Reax FF was simulated by LAMMPS program, and the corresponding C program was written to deal with the results of the simulation. The distribution of products containing nitrogen gas and the nitrogen element reactions occurred in the simulation process were analyzed. The simulation results are in good agreement with the experimental results, for example, there are few nitrogen oxides in lignite pyrolysis system and hydrogenation system, and the nitrogen products are mainly HCN-NH _ 3 and nitrile compounds, and a large number of nitrogen oxides are formed in oxygen-added pyrolysis system, the nitrogen oxides are mainly no _ 2. The results show that the intermediates of CH2NH molecule, such as NH radical, Con radical and CN radical, can be formed during pyrolysis. In the hydropyrolysis system, the hydrogen can interact with the hydrogen to form HCNN NH 3, and in the oxygen-added pyrolysis system, no can be formed by the interaction with oxidant. This study provides a reliable theoretical basis for the study of nitrogen conversion mechanism in the process of gasification and liquefaction of brown coal.
【学位授予单位】：华北理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ530.2;TD849.2

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