基于分子动力学模拟的植物绝缘油过热分解产气特性

Gas Production Characteristics of Vegetable Insulating Oils Under Thermal Decomposition Based on Molecular Dynamic Simulation

为更好地了解植物绝缘油的产气过程,指导植物绝缘油变压器故障诊断,从宏观和微观两个层面研究了山茶籽绝缘油的热分解过程。通过实验研究了山茶籽绝缘油在363～403 K温度下经过5、10、15、20天热分解的产气特性和酸值变化规律。采用Reax FF反应力场构建山茶籽绝缘油模拟体系,通过分子动力学（MD）仿真,模拟植物绝缘油中分子在1400～2200K温度下的分解过程,得到其产物信息;并通过跟踪观测模拟体系中的分子变化,得到其产气路径和机理。实验和仿真结果表明：C2H6是山茶籽绝缘油在热解时产生的主要烃类气体产物;含非共轭双键越多的甘油三酸酯分子热稳定性越差,越容易分解;温度升高和受热时间增长能够促进植物绝缘油的分解,产生各种特征气体含量与温度和受热时间呈正相关;就产气路径而言,植物绝缘油热解是从与甘油三酸酯分子中心碳相连的C—O键的断裂开始,然后通过脱羧反应生成CO2和烃类自由基,烃类自由基继续分解,并与分解过程中产生的H·结合,得到植物绝缘油分解的各种特征气体。

In order to understand the gas generation process of vegetable insulating oils and guide fault diagnosis of transformers, the macroscopic experiment and microcosmic molecule simulation of camellia oil thermal decomposition process were studied. Thermal decomposition experiments of camellia insulating oil from 363 K to 403 K during 5, 10, 15, and 20 days were conducted, and gas production characteristics and acid value change rules were obtained. Moreover, the molecular model system of camellia oil was established, the molecular dynamics simulation based on ReaxFF（Reactive Force-Field） was adopted to analyze the pyrolysis process of molecules in oil from 1 400 K to 2 200 K, and the product formation was obtained. In addition, gas production generation paths and mechanisms were obtained through tracking observation of molecules in the reaction system. The experiment and simulation results show that C2 H6 is the main hydrocarbon gas of camellia insulating oil under thermal decomposition. The more unconjugated double bonds the triglyceride have, the poorer the thermal stability will be, and the more easily a molecule will decompose. The increase of temperature and heating duration promotes the decomposition of oil, and contents of characteristic gases are positively related to the temperature and the heating duration. For gas production path and mechanism, it is found that the C—O bond which connects to the center carbon of triglyceride molecule is broken at the beginning of the reaction, then the CO2 and free radicals of hydrocarbons are generated through decarboxylation reactions, the free radicals of hydrocarbons continue to decompose and are combined with H·, then various characteristic gases generated by pyrolysis of vegetable oils are obtained.