【作者】 周禹成；

【导师】 吴嘉；

【作者基本信息】 浙江大学 ， 化学工程， 2010， 硕士

【摘要】 精馏过程是化工工业中耗能最大的单元操作之一,在当今能源价格持续上涨的情况下,精馏操作能耗的降低便具有极其重要的意义。而热集成与精馏的结合作为节能的一种主要方法,其发展和应用也受到了广泛的关注和较为深入的研究。本文针对植物多糖提取液的精制分离过程,提出一种新型的DVH流程。通过精馏塔侧线出料和蒸汽喷射泵的结合,完成蒸发过程并回收了蒸汽潜热,将精馏、蒸发和热泵三个操作单元进行集成,不仅节约了一个蒸发器,节省下了设备费用,并且通过产品蒸汽潜热的再利用,使DVH流程比传统流程的能耗降低34%以上。但是同时,新流程增加了系统的耦合程度,给生产过程中的控制和系统的开车带来了很大的难题,为了能够实现新流程的工业应用,对其进行详细的可控性分析和动态行为研究是必要的。本文展开了严格机理模型的建立、动态行为研究、可控性分析、控制结构的选择和闭环动态响应的比较、开车方案的设计和开车过程的模拟优化等研究,具体的内容包括：1.采用商业模拟软件Aspen Plus中的严格非线性模型对DVH流程进行稳态模拟,在模拟中精馏塔采用Radfrac模块,并且应用了严格的水力学计算方法。换热器都采用独立的换热器Heatx模块。所有单元操作模块的计算所需数据均根据工厂实际设备参数选取。并通过Aspen Plus结合分布式并行遗传算法计算出系统在稳定生产时的最优操作参数；2.采用Aspen Dynamics和Aspen Custom Modeler对DVH流程进行动态建模,并对系统对于操作变量扰动及进料和蒸汽扰动的开环动态响应进行分析,观察系统变量之间的相互关系,总结其开环动态特性,并根据流程的特点建立起可能的控制结构；3.本文采用相对增益矩阵、NI准数和MRI准数来对不同控制结构的传递矩阵进行对比分析并判断系统的可控性,从而选择出较优的控制结构来做进一步的讨论；4.针对上述的控制结构,本文对浓度直接控制和预测控制两种方案及不同混合蒸汽压力的状态在操作变量扰动及进料和蒸汽扰动情况下的闭环动态响应进行了分析,选择出了在不同扰动下的最佳控制方案,并总结了各种控制方案的优势和不足；5.最后,本文对DVH流程进行了解耦,提出了一种独特的开车方案,以工艺软水作为初始进料,在蒸汽喷射泵可以提供稳定热源后再将提取液作为进料。并通过对开车过程进行动态模拟,获得了系统随时间的变化趋势和较佳的操作参数。同时,对塔顶和塔底的出料时间及出料浓度进行了优化,避免了不合格产品需要循环进入系统的问题,保证了系统的稳定性,并实现了原料提取液的零损失和废料的零排放。更多还原

【Abstract】 The distillation is one of the most energy-consuming unit operations in the chemical engineering and industry. Nowadays, since the price of energy source keeps increasing, it is of great significance to reduce the energy consumption of distillation operation. As the main approach to energy-saving, the distillation with the heat integration has gained intensive concern and further study in the aspect of development and application.In this dissertation, a novel DVH process is proposed for the purification and separation process of plant polysaccharide extract. By means of combination of side draw of distillation column and vapor jet pump, the evaporation process is accomplished, at the same time, the latent heat of vapor is recycled. The integration of the three unit operation unit-distillation, evaporation and heat pump, not only saves one evaporator and then decreases the equipment cost, but also makes the DVH process reduces the heat consumption by at least 34% compared with the traditional process, by the recycle of the latent heat of product vapor. However, at the same time, this novel process increases the coupling of the system, and leads to significant difficulties in the control during operation of production and start-up. It is necessary to study the dynamic behavior and controllability analysis of this novel system on purpose of industrial application.In this dissertation, a high-fidelity model is developed, dynamic behavior is studied, control structure is selected, the closed-loop dynamic behavior of different control schemes are compared, the start-up scheme is designed, and the start-up process is simulated and optimized. The detailed research work and contributions of this dissertation are as follows:1. The steady-state simulation of DVH process is completed using rigid non-linear model in the commercial simulation tools Aspen Plus. In the simulation, distillation column uses RADFRAC models with rigorous hydraulics method. The heat-exchanger use independent Heatx models. All the parameters needed in the calculation of unit operation are derived from the practice factory data. The parameters in the steady-state run are optimized by the method of Aspen Plus coupled with a distributed parallel genetic algorithm.2. The dynamic process of DVH is simulated using the software Aspen Dynamics and Aspen Custom Modeler. The detailed open-loop dynamic behavior study about the feed stream and manipulating variables disturbances is proposed to analyze the interaction between system parameters, and summarize the open-loop dynamic behavior characteristic of the system to establish suitable control structure.3. The transfer matrices of different control structures are compared and analyzed using the relative gain matrix and dimensionless number NI and MRI, the controllability of the system is judged, and then the better control structure is picked out for the further study.4. Specific to the above-mentioned control structure, in this dissertation, the closed-loop dynamic behavior study about the operation parameters and feed stream or vapor pressure disturbances are analyzed with different mixed vapor pressure separately using the control strategy-direct composition control and predictive control. Under different disturbances, the best control strategy is chosen, the advantages and disadvantages of each control strategy are summarized.5. Finally, in this dissertation, DVH process is decoupled, a special start-up strategy is proposed, soft water from the process is set as initial feed, when the steam jet pump can supply sufficient heat, extract is then set as feed. The trend of the system changing with time and better operation parameters are achieved by the dynamic simulation of the start-up. At the same time, the out-put timing and composition of both column top and bottom are optimized, avoiding the recycle of the disqualified product and make sure the stabilization of the system. At the same time, the extract gets zero loss and no waste discharged.更多还原