【作者】 金洪鑫；

【导师】 潘海；

【作者基本信息】 浙江工业大学 ， 化学工程， 2010， 硕士

【摘要】 熔融指数是聚丙烯生产过程中最重要的质量指标。由于工艺设备以及技术上的原因,熔融指数难以在线测量,从现场采集聚丙烯产品样品进行化验则会造成测量滞后的存在,导致无法对熔融指数进行有效在线控制。针对聚丙烯生产过程熔融指数测量存在的难题,提出一种组合神经网络软测量建模方法,并用于建立熔融指数的软测量模型。本文的主要研究内容如下:(1)首先简单介绍了聚合过程的特点,以及聚合反应过程研究存在的问题。探讨了软测量技术在聚合反应过程应用的可行性和意义。介绍了软测量技术的基本思想和实现步骤,并对各种软测量建模方法及其在工业领域中的应用现状进行了综述,并指出软测量技术在处理强非线性和不确定性对象时还有待完善。(2)具体分析了常用的BP神经网络算法,包括BP网络结构和BP训练过程及算法。针对人工神经网络在建立非线性对象模型时的缺点,引入组合预测方法。对组合预测的研究现状、分类、组合系数的确定进行了详细的介绍。最后将神经网络与组合预测方法相结合提出了组合神经网络,并将最小化最大绝对误差作为求解组合权重的准则,提出了基于最小化最大绝对误差的组合神经网络建模方法。(3)综合分析Spheripol工艺的催化剂体系、均聚反应机理和生产工艺流程,确定影响熔融指数的辅助变量。其次,对选取的样本数据进行预处理,包括异常数据剔除、随机误差处理和数据归一化。随后采用经验法和凑试法相结合,确定了BP网络隐含层的数目和节点数。最后采用组合神经网络建模,并将组合神经网络同单一BP神经网络进行性能比较,通过比较分析说明了组合神经网络的有效性。更多还原

【Abstract】 Melt index is the most important indicator of quality in the production process of polypropylene. Because of the constraints of process equipment and technical, the melt index is difficult to measure online. If we directly measure the melt index of the polypropylene product samples, that will result the measurement delay, melt index can not be controlled effectively online. Because the melt index is difficult to measure online, model of melt index prediction based on stacked neural networks was established.This article mainly includes the following:(1) Above all, introduced the characteristics of the polymerization process and problem of polymerization process study. Discussed the feasibility and significance of soft sensor. Introduced the basic idea of soft sensor and its implementation steps, generally described the situation of various soft sensor modeling method and its application in the industrial field.(2) Analyzed some commonly artificial neural network algorithm, including the RBF neural network and BP neural network. Because of the defect of establishing a nonlinear model base on artificial neural network, introduced combined forecasting method. Detailedly described the status quo, classification and combination coefficient of combined forecasting. Finally, proposed stacked neural networks based on neural network and combined forecasting methods, and to minimizing the maximum absolute error as the criteria for solving the combination weight. Proposed the combined neural network modeling based on minimizing the maximum absolute error.(3) Integrated analysed the catalyst system of Spheripol process、homopolymerization mechanism and production process, determine auxiliary variables of impacting melt index. Secondly, preprocessed sample data, including different date exclusion, random error processing and data normalization. Then, determined the number of BP network hidden layer and nodes based on experience piece-try method. Finally, build combined neural network model, and through comparing combined neural network with a single BP neural network, proved the effectiveness of combined neural network.更多还原