【作者】 周志超；

【导师】 吴嘉；

【作者基本信息】 浙江大学 ， 化学工程， 2008， 硕士

【摘要】 甲醇是仅次于烯烃和芳烃第三重要的基础化工原料。近年来甲醇在新型能源特别是燃料电池和汽车燃料方面的用途得到了良好的开发,其需求量与产能也随着新用途的开发迅速提高。在合成甲醇工业生产过程中,粗甲醇的精制不仅是决定甲醇产品质量的重要工序,而且也是影响甲醇生产成本的关键因素之一。因此甲醇精制工艺节能和节水研究,是具有重要的实际意义。随着全球能源危机所引起的成本压力,目前我国普遍采用节能型的三塔双效精馏工艺精制甲醇。本文的研究对象是2005年吴嘉和陈露提出的一种新型双效精馏工艺(NLSF),与传统的工艺相比,新工艺能够节约能量24.7%,节约软水约38.0%。但是同时新工艺增加了系统的耦合程度,加强了两个塔之间的关联性,提高了系统对于进料波动的响应的复杂性,给控制带来了很大的难题。为了能够实现新工艺的工业应用,对新工艺进行详细的动态行为研究和可控性分析是必须的。本论文展开了严格机理模型的建立、模型参数寻优、动态行为研究、可控性分析和闭环动态响应的比较以及与文献中提到的两种典型的双效精馏工艺(LSF和FS)进行对比。详细内容包括:1.热集成双效精馏工艺的稳态和动态机理模型方法的介绍。在建立机理模型过程中充分考虑到新工艺操作变量相互耦合的复杂性,利用商业模拟软件Aspen Plus与Aspen Dynamics建立了新工艺的稳态和动态模型。为了使模型严格可靠,精馏塔模拟采用了考虑水力学影响的RADFRAC模块,精馏塔的换热器和冷凝器都采用独立的换热器Heatx模块,并以实际甲醇精制工艺中的设备参数和进料参数为模型参数。2.为了对三种工艺稳态模拟结果进行比较,必须首先解决操作参数求解的问题。热耦合双效精馏系统优化是一个强约束下多变量优化的难题,本论文采用模块化结合分布式遗传算法实现稳态最优化设计,求出LSF,FS和NLSF三种工艺操作参数。并对优化后三种工艺的能耗和产品质量进行分析比较。3.对于NLSF这种热耦合双效精馏结构,系统中变量之间的耦合非常严重,为了建立合适的控制方案,必须对系统的动态行为进行研究。本论文对系统对于进料扰动和操作变量扰动的开环动态响应进行详细研究,观察系统变量之间相互关系,总结新工艺的开环动态特性,并结合实际情况建立合理的控制策略。4.分析和比较新工艺的不同控制方案的控制效果,进行可控性分析是必须的。本论文采用一些相关的准数对系统进行可控性分析,利用可控性分析结果对控制方案的控制效果进行预测。以几种进料扰动为代表,比较新工艺不同控制方案下的闭环动态响应,对可控性分析的结果进行验证并选出最优的控制方案。5.为了更加深入的了解新工艺的动态行为特点和指导甲醇精馏工艺的选择,本论文对LSF,FS和NLSF三种工艺分别建立不同的控制策略,进行了可控性分析和闭环动态行为的研究,选择出最佳的控制方案。并在相同的进料扰动下,比较在各自最优控制方案下三种工艺的动态响应曲线。最后,对全文的工作进行总结,并且提出了进一步研究的方向。更多还原

【Abstract】 Next to alkene and arene, methanol is the third massive organic product in chemical industry. Recently the uses of methanol for new sources of energy, especially for the fuel cell and the fuel of vehicles, have been in practice applications and are developing widely. Accompanied by this development, the market demand and the capacity of production of methanol are increasing rapidly. In the synthesized methanol industry, the purification of raw methanol is not only the important process determining the quality of product, but also a key factor influencing the energy cost of production. It is important for promoting the development of methanol production to study the new techniques for distillation of methanol with saving the energy and water consumptions. Along with the cost increase bringing by global energy source crisis, the 3-column double-effect distillation process has been widely adopted in China due to its ability of reducing energy consumption and annual cost.A novel double-effect distillation process (NLSF) reported by Wu and Chen (2005) has been studied in detail in this dissertation. Compared with the traditional 3-column double-effect distillation process widely used today, this novel process could reduce the heat consumption by 24.7% and soft-water consumption by 38.0%. However, this novel process enhances the coupling of different units in the system and the interactions between the two distillation columns, which results in the complexity of system responses to feed disturbances and increases significant difficulties in operation and control. Therefore, it is necessary to study the dynamical behavior and controllability of this novel double-effect distillation scheme before putting it into implementation of industrial application.In this dissertation, a high-fidelity model of NLSF process was developed first with the model parameters optimized. Then with this model, the open-loop dynamical behavior of NLSF was studied, the controllability analysis was carried out, a few of possible controlling schemes were proposed, the closed-loop dynamical behaviors of these schemes were studied with comparisons. At last, the difference of dynamical characteristics and controllability between NLSF and the other classical processes (LSF and FS) were also compared. The detailed work and main contributions of this dissertation are as follows:1. The rigorous steady-state and dynamic models of NLSF process were setup on chemical engineering principles with the coupling characteristics considered sufficiently and by use of the commercial software Aspen Plus and Aspen Dynamics. In order to make the dynamical model more reliable and rigorous, two distillation columns were simulated by RADFRAC models and their reboilers and condensers were simulated by independent HeatX models with rigorous hydraulics method and the equipment and feed stream parameters derived from the practice factory data.2. It is crucial to solve the optimization of steady-state models of the three processes for comparing their performances. The optimization of heat-integrated double-effect distillation system is a puzzle of optimization of multivariable nonlinear function with strong constraints. The method of distributed parallel genetic algorithm coupled with a sequential modular process simulator was employed to optimize the parameters of LSF, FS and NLSF processes. The energy consumption and product quality of the three optimized steady-state processes were analyzed comparatively.3. For the NLSF process of heat-integrated double-effect distillation, the coupling between variables is heavily, so it is necessary to study the dynamical behavior of system in order to setup proper control strategy. A detailed study on the open-loop dynamical response of the system to disturbances of feed and operation variable were carried out by observing the interrelations of system variables. On the summation of open-loop dynamical characteristics of NLSF and the combination of practice situations, several rational control strategies were proposed.4. The controllability analysis is necessary to compare the performances of different control strategies for NLSF. A few related control indexes were adopted in controllability analysis to predict and to distinguish the performances of different strategies. Six feed disturbances were chosen as the representatives of the real operating situations. The closed-loop dynamical performances of different control strategies under these disturbances were studied comparatively to check the results of controllability analysis and to find the best one.5. In order to understand the characteristics of the dynamical behavior of NLSF and to guide the choice of industrial methanol distillation process, the controllability analysis and the closed-loop dynamical behavior studies were carried out with different control strategies for LSF, FS and NLSF processes respectively. The optimal control strategy of each process was found. Then a comparative study on the dynamical response curves was carried out for the three processes with their own optimal control strategies.At the end of dissertation, the conclusions of present work and suggestions for further research were given.更多还原