Abstract: A model of grade transition is presented for the industrial high-density polyethylene (HDPE) continuous slurry process, which has two reactors and one pelletizer connected in series.The object of the model is to minimize the quantity of off-specification product and the time of grade transition.By the optimization of the objective function, the trajectories of both the controlled variables and the quality target of polymer product can be obtain, such as polymerization temperature, hydrogen to ethylene ratio(［H₂］/［C₂］), co-monomer butylene to ethylene ratio(［C₄］/［C₂］), catalyst feed rates, the quality target of polymer product in the two reactors and the polymer’s melt index(MI) in the pelletizer.The result showed that the polymer grade was determined by the properties of both the polymer slurry from the reactors and the polymer pellet from the pelletizer.Therefore, the grade transition strategy must be optimized from a plantwide viewpoint.The factor of pelletizer was added into the objective function, which effectively restrained the sharp change of controlled variable and ensured the security of the grade transition process.

摘要： 针对淤浆法乙烯聚合工艺串联生产过程，以切换时间最短和产生废料量最少为目标，对“反应釜-反应釜-造粒机”三者串联过程，建立了包括后处理过程在内的牌号切换优化模型.并利用迭代动态规划法对目标函数求解，得到各反应釜中聚合温度、氢气与乙烯单体浓度比(［H₂］/［C₂］)、共聚单体丁烯与乙烯单体浓度比(［C₄］/［C₂］)、催化剂进料流率4个操作变量和聚合物产品各性能指标的变化轨迹以及造粒机中聚合物熔融指数(MI)的变化轨迹.研究表明，聚合物的性能指标由反应过程和造粒过程共同决定.在目标函数中考虑造粒过程的影响后，能够有效抑制操作变量的剧烈变化，使其变化轨迹趋于平缓，保证切换生产过程的安全进行.