醋酸脫水之整廠設計與控制

Plantwide Design and Control of Acetic Acid Dehydration Process

李季儒(Chi-Ju Lee)

指導教授 ： 鄭西顯 ； 王聖潔

國立清華大學/工學院/化學工程學系/碩士(2006年)

摘要

本研究以國內耗能量甚大的醋酸脫水製程為對象，探討進料中包含雜質-乙酸甲酯與對位二甲苯之整廠省能設計與整廠控制策略。
在整廠省能設計方面，由於醋酸與水沸點相近，本研究以非均勻相共沸蒸餾技術分離此近沸混合物，藉夾帶劑乙酸異丁酯之添加使分離程序容易進行，同時減少傳統蒸餾所需之能源。並進一步使用完全熱整合省能技術，以隔牆塔分離水相之三個產物-水、乙酸甲酯與乙酸異丁酯，如此可減少蒸餾塔硬體設備費用，且模擬結果顯示隔牆塔不但比傳統塔節省約28%的能源消耗，還能分離出純度較高的產物。
在整廠控制策略方面，本研究利用作動變數為夾帶劑補充量與再沸器熱負載之兩個溫度控制環路的執行，使醋酸脫水塔塔底醋酸與水相醋酸濃度符合規格，並以SVD與閉環路分析選擇兩個控制板層，發現進行夾帶劑容量控制時之設定點不需要改變，且可從此分析中挑選出所需夾帶劑補充量最少的板層位置。但再沸器熱負載的控制環路，其設定點則需改變，本研究利用外環路為塔底溫度之串級控制策略執行，使產品符合規格。在隔牆塔部份，則是利用SVD與RGA挑選並配對作動變數與控制變數，所建立的三個溫度控制環路在設定點不需更改的情況下，即可維持隔牆塔三個產品純度。

關鍵字

醋酸脫水 ； 非均勻相共沸蒸餾 ； 熱整合塔 ； 整廠

並列摘要

The separation of water and acetic acid is one of high energy consuming processes. This research studies a various strategies of energy saving in such a commercial process which contains impurities of MA and PX. Since the normal boiling points of water and acetic acid are very close, the best way to separate them is to use an entrainer, iso-butyl acetate in this case, to change their relative volatility. Using heterogeneous azeotropic distillation requires much less energy than the conventional distillation.
We also propose the newly developed technology, thermal coupled distillation column, to separate three components. The study results show that the thermal coupled distillation column, divided wall column, not only reduce the capital cost, but also save energy as high as 28% compared with the conventional column.
The manipulated variables are entrainer makeup and reboiler duty used to implement two temperature control loops to obtain the products purities of acetic acid dehydration column. SVD analysis is also used to choose two controlled stages, and we find that the set point of the controlled stage isn’t needed to be changed under entrainer inventory control. However, the set point of the other stage controlled by reboiler duty is needed to be changed, thus we use cascade control to solve this problem. About DWC, we use SVD and RGA to build the control strategy and we can obtain the products purities under these three temperature control loops.

並列關鍵字

acetic acid dehydration ； heterogeneous azeotropic distillation ； thermally coupled distillation column ； plantwide

參考文獻

Abdul Mutalib, M. I., Smith, R. (1998) Operation and Control of Dividing Wall Distillation Columns. Part 1: Degrees of Freedom and Dynamic Simulation. Trans. Inst. Chem. Eng., 76, 308-318

Abdul Mutalib, M. I., Smith, R. (1998) Operation and Control of Dividing Wall Distillation Columns. Part 2: Simulation and Pilot Plant Studies Using Temperature Control. Trans. Inst. Chem. Eng., 76, 319-334

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