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Mathematical modeling of a high-pressure ethylene
polymerization tubular reactor |
| ZHANG Lei-ming, WANG Jing-dai, YANG Yong-rong |
State Key Laboratory of Chemical Engineering, UNILAB Research Center for Chemical Reaction
Engineering; Department of Chemical and Biochemical Engineering, Zhejiang University, Hangzhou 310027, China |
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Abstract A mathematical model for an industrial low-density polyethylene (LDPE) tubular reactor was established in order to investigate the distribution of important variables inside the reactor. The model was built by moment method based on the kinetics of freeradical polymerization and combined with mass, energy and momentum balance. The profiles of variables along the reactor including temperature of processing stream, concentration of initiators, conversion, number and weight average molecular weight and melting index of LDPE could be determined by solving the model. The model was proved accurate compared with industrial data such as temperature, ethylene conversion and melting index at reactor outlet. Meanwhile, the profile of temperature along the reactor predicted by the model can reflect the fouling condition inside the reactor and provide indication or supervision for fouling. To sum up, the model with the swiftness and high accuracy can be employed as soft sensor and on-line monitor for industrial plant; therefore, it can provide reliable information for operation optimization, decision making and accident prevention．
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Published: 16 March 2012
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高压法聚乙烯管式反应器的数学模拟
为了研究高压聚乙烯管式反应器内各重要变量沿管程的分布,基于自由基聚合反应机理,结合质量、能量和动量守恒,采用矩方法对其进行了数学建模.通过对模型的参数优化和求解,获得了反应器内物料温度、引发剂浓度、转化率、聚合物重均及数均摩尔质量和熔融指数沿管程方向的演化过程.同时,通过反应器内物料的温度变化、出口转化率和产品熔融指数与工业数据的对比,发现计算值与工业实际值符合良好,验证了模型的精确性.此外,模型的温度预测可以反映管内的黏壁问题,为黏壁状态提供检测和指示.模型运算简便快捷且准确度高,能实现工业反应器的软测量和在线监测,为优化操作过程、制定生产决策、预防事故发生提供可靠依据.
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