結合蒸餾塔與液-液分離單元之系統的設計與控制

Design and Control of Systems Utilizing Distillation Columns and Liquid-Liquid Separation Units

易均正(Chun-Cheng Yi)

指導教授 ： 錢義隆

國立臺灣大學/工學院/化學工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201802373

摘要

本文探討兩類混合物分離程序的設計與控制，分別為環己烷與環己烯近沸混合物分離程序以及甲醇、甲苯與水三元共沸混合物分離程序。此二程序皆由蒸餾塔與液-液分離單元所組成，相較於現有文獻所描述的他種分離方法，本文所提出的分離程序皆能有效降低能源消耗以及年度總成本。環己烷與環己烯間的相對揮發度非常小，因此一般的蒸餾程序幾乎無法達成兩者的分離。透過引入適當的夾帶劑，萃取蒸餾系統能在符合經濟效益的情況下將兩者分離開來，另外熱整合策略的實施可以使該系統節省下可觀的操作成本和能源消耗。為兼顧經濟性和可控制性，系統的操作條件由最適化分析和閉環靈敏度測試的結果共同決定。根據動態模擬顯示的結果，該系統在設計的控制架構下可以有效排除進料流率和組成的擾動，使產物純度維持在設定規格左右。
　　甲醇、甲苯與水為三元共沸混合物，一般的蒸餾程序無法將三者完全分開，而本文所提出的分離程序由萃取塔和蒸餾塔組成，首先透過將水做為溶劑的方式施行溶劑萃取以分離出高純度甲苯產物，接著利用蒸餾塔完成甲醇與水的分離並回收大部分水重新做為溶劑。由於水本來就是待分離的成分之一，該萃取過程並不會引入新成分，因此可以避免產物受到汙染的可能性。該系統充分利用了成分間的不相容性來突破蒸餾邊界的限制，整個程序中只用到一支蒸餾塔故能源消耗和操作成本比文獻中提到的分離方法低上許多，整體架構也更簡單可行。在動態控制上，開環靈敏度測試和閉環靈敏度測試的結果為控制架構的設計提供了關鍵性的指標。經過動態模擬的驗證，該系統在設計的控制架構下可以有效排除進料流率和組成的擾動，使三股產物流的純度都維持在設定規格左右。

關鍵字

近沸物 ； 共沸物 ； 萃取蒸餾 ； 溶劑萃取 ； 程序設計 ； 程序控制

並列摘要

Design and control for the separation processes of two kinds of mixtures will be discussed in this thesis, including cyclohexane/cyclohexene close-boiling mixture and methanol/toluene/water ternary azeotropic mixture. These two processes are both composed of distillation columns and liquid-liquid separation units. Compared to the separation methods mentioned in the references, processes proposed in this thesis provide significant reduction in energy consumption and total annual cost. Relative volatility between cyclohexane and cyclohexene is extremely low, hence it is impractical to separate these components by the conventional distillation process. By introducing an appropriate entrainer, extractive distillation system is capable of separating these two components economically. Furthermore, energy consumption and operating cost of this system can be considerably reduced by performing heat integration. Considering the trade-off between economic and controllability, operating conditions of the system are determined by investigating the results of optimization analysis and closed-loop sensitivity test. The responses of dynamic simulations show that this system can reject disturbances in feed flowrate and feed composition effectively under devised control structure, so that product purities can be maintained nearly at their specification.
　　Methanol, toluene and water form ternary azeotropic mixture which cannot be separated by conventional distillation process. In this thesis, a separation process composed of an extraction column and a distillation column is proposed for this task. Toluene product with high purity is firstly separated by performing solvent extraction using water as solvent. The following step is separating methanol from water by a regular distillation column and recycling most of the water for the purpose of solvent extraction. Because water itself is the component being separated, the solvent extraction process will not introduce any foreign component and hence avoid the possibility of contaminating products. This system fully utilizes the heterogeneity of components to cross the distillation boundary so there is only one distillation column needed in the whole process. Hence, energy consumption and operating cost of this process are much lower compared to that of separation method mentioned in the reference and the whole structure is simpler and more feasible. As for the dynamic control, results of open-loop and closed-loop sensitivity tests provide critical index for the design of control structure. Confirmed by the results of dynamic simulations, this system can reject disturbances in feed flowrate and feed composition effectively under devised control structure so that purities of three product streams can be maintained at their specification.

並列關鍵字

close-boiling ； azeotrope ； extractive distillation ； solvent extraction ； process design ； process control

參考文獻

參考文獻

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