【作者】 王林；

【导师】 王树青； 李浦； Guenter Wozny；

【作者基本信息】 浙江大学 ， 控制科学与工程， 2002， 博士

【摘要】 间歇精馏生产过程中，冷启动操作是极其重要的环节。不仅因为有大量的设备需要开始投入使用，而且在工业现场的每个生产批次中，料液组成，加热方式，塔顶回流的操作方式都有可能发生变化。然而在没有动态模拟的情况下，启动过程主要根据经验进行操作，不可能、也不允许直接在装置上做任何试验。 应用动态模拟技术，探讨、分析间歇精馏启动过程的特性，其主要作用有： 1) 缩短启动时间，使设备尽快达到稳定操作状态； 2) 降低物耗、能耗，减少启动损耗； 3) 避免可能产生的误操作或事故； 4) 减少不合格产品； 5) 保证启动过程顺利进行，取得最佳经济效益； 动态模拟的核心是系统模型。以往间歇精馏塔的动态模型大部分建立在平衡模型的基础上，由于它采用了大规模的微分代数方程组，所以使系统的初始化成为一个难题。 本文从过程特性分析、建模、求解和实验验证四个方面，对间歇精馏冷启动过程的动态模型进行了描述，具体包括以下几个部分： 1．分析间歇精馏塔从冷、空状态启动时的过程特性。针对塔板的动态特性以及塔板间的变化关系，将启动过程描述为三种状态之间的切换，即：冷空状态(EM)、液体积累状态(LA)、汽液平衡状态(VLE)。塔板温度和塔板积液作为沿空间轴(底层塔板到上层塔板)和时间轴不断发生变化的动态变量，它们共同决定了塔板上汽液平衡状态的建立。通过实验观察和现象分析，得到两个重要结论： a．汽液平衡状态的建立是从下到上逐板发生的，这集中体现在塔板温度的变化曲线上。 b．塔板积液的主要增长是由回流决定的。 2．采用具有时间一致性的动态模型描述间歇精馏塔的启动过程。以分离过程的重要设备—塔板为例，每层塔板都是从非平衡状态，即只有能量和物质交换， 11 浙江人学博上学位论文转化到平衡状态，即到达汽－液平衡。而转换点是山工作压力下的泡点温度决定的。通过塔板的结构特性，利用不同的溢流堰高度描述了塔板积液的变化情况。在传统MESH方程的基础上，结合启动过程特性和塔板动力学方程，能够很好地描述塔板在EM—LA—VLE切换过程中的变化情况。采用模块化方法进行系统建模，使模型结构清晰，易于拓展。 3．分析模型中的混杂性问题。文章对求解过程中呈现的非连续特性进行了分类，即：与启动过程状态转换有关的模型结构的不连续性，与物理过程有关的塔扳动力学方程的切换，给出了针对不同类型非线性特征的解决方案。对于动态模型所涉及的变量初始值问题，以及状态切换过程中变量取值的变化，文章先对变量进行了分类，然后给出了不同类型变量的初值选取方法。为了更多地关注于过程，而不是模型的复杂性和求解的难度，选用gPROMS作为计算平台用于求解该过程。 4．通过仿真实例验证了动态模型仿真结果的有效性和正确性。第一个仿真实例是一个非常著名的三组分间歇分离过程，针对如何确定优化起始点这个问题，通过比较实验数据和简化方法求解结果，说明了模型的有效性和可操作性。第二个仿真实例是一个具体的实验装置，针对间歇精馏塔启动过程中的动态特性，通过实验过程数据和仿真结果的比较，验证了模型的正确性。仿真结果同时表明：间歇精馏塔从冷。空状态启动时过程动态的复杂性，和动态模型中的高度非连续性特征。 最后对论文结果的工业应用前景给出了作者个人的看法，总结了论文工作的创新之处，以及讨论了本课题需进一步研究的问题。更多还原

【Abstract】 Due to its high flexibility the batch distillation is widely used in chemical industry. A property of batch distillation is that the batch column will be frequently started up from a cold empty state. The initial charge in the reboiler, heating style and reflux operation may be variable from batch to batch. The performance of startup from these initial conditions will impact the whole batch operation. Therefore, the study of startup behaviors of batch distillation is important to industrial practice. Modeling of batch distillation has been mostly based on equilibrium model in previous studies. It leads to a large-scale differential algebraic equations (DAEs) system. Due to its dynamic nature, initialization of the system has been a problem. A model to express startup behaviors of batch columns starting from an empty cold state is proposed to handle these issues.For each tray, we can get its dynamic feature through observation and analysis of the phenomena on the tray. At the very beginning we define the trays in the column are at the state of empty (EM). Then the tray is transited from EM to the state of liquid accumulation (LA), due to the condensation of the rising vapor on the tray. At the same time the condensed liquid on this tray is heated by the rising vapor from the reboiler. When the temperature increases at its bubble point, the state of the tray switches to vapor-liquid equilibrium (VLB). The sequence of the transitions of a tray is from EM to LA and VLB. When the vapor arrives in the total condenser, the holdup of the trays will be increased significantly after the reflux valve opened. The startup is ended when the liquid flow reaches the lowest tray of the column, which means that all trays are in VLE and have an enough liquid holdup. The startup features are common to general batch tray columns. The fact that the temperature rises tray by tray from bottom to top and the column is filled with the liquid flow essentially from top to bottom during startup is well-known in industry practice.A unified equation system can describe the switching from a non-equilibrium phase in which only mass and energy transfer are taking place to an equilibrium phase inwhich the vapor-liquid equilibrium is held. The switching point between these two phases is decided by the relationship of bubble point temperature at the operating pressure. The liquid holdup of each tray is related to the geometry of the trays, different weir height is used to describe the holdup change during startup period. The model for startup operation appears discontinuous between nonequilibrium and equilibrium phase. The structure discontinuous mode of the model related with the working state of the column during startup operation. But to a unified equation system, the structure of differential equations must be set to the same in all different phases. So trivial equations are introduced to realize this aim. In the numeric method, three types of variables are divided, company with three different ways to set variables’ initial value. The software package gPROMS is used for solving the equations system. It is unique amongst commercial simulators in its facilities for describing hybrid processes with discontinuities.Two cases are used to validate the correctness of the model. The first process considered is a well-known batch distillation given by Nad and Spiegel (1987). The second is a pilot batch column in lab. It can be seen that the model can describe the startup process with a high accuracy by the comparison of the simulation results and experiment data. The dissertation is concluded with a summary and prospect of future researches.更多还原