Design and Control of Distillation Processes to Separate Azeotropic Mixtures Aided by Liquid-Liquid Separation
|關鍵字:||程序設計與控制;共沸物分離;複合分離程序;蒸餾;萃取;甲基丙烯酸甲酯;正丙醇;Process Design and Control;Azeotropic Separation;Hybrid Separation Process;Distillation;Extraction;Methyl Methacrylate;n-Propanol||公開日期:||2016||摘要:||本研究共分兩部份：一為分離含有甲基丙烯酸甲酯、甲醇與水的混合物之程序，另一部份為萃取/蒸餾複合程序的深入研究，並以正丙醇去水作實例研究。 第一部份中，在使用與原始雙塔設計相同的程序單元、但不同設計架構之下，本研究對一種節能雙塔設計用來分離含有甲基丙基酸甲酯、甲醇與水的混合物進行詳細的研究，藉由設計常規蒸餾塔的塔頂及塔底組成分別於系統的不穩定及穩定節點上，結果顯示相較於原始雙塔設計將塔底設計在系統之鞍點，蒸汽成本可大幅節省16.3%，而此節能雙塔設計另一項好處為隨著純水物流而出的甲基丙基酸甲酯產物損失亦比原始設計少，代表著額外9.6%的操作成本節省。再者，本研究同時考慮開環路與閉環路敏感度測試的結果，創新提出此節能設計的整廠控制架構，藉由控制常規蒸餾塔中兩塔板的溫度差以及汽提塔中另一個單點板溫控制，無論在新鮮進料流量或組成發生巨大改變之下，甲基丙烯酸甲酯與水產物皆能維持在高純度。 本研究另一部份中是關於萃取/蒸餾複合程序的充份研究，藉由結合液-液分離以及蒸餾的技術，此複合系統可視為非均勻相共沸蒸餾的衍生型程序，而實行萃取/蒸餾複合程序所帶來巨大的節能潛力將以概念簡介與正丙醇去水的實例來作說明。考慮其合適的密度、汽化熱、低毒性，異丙醚被選為實例中的萃取溶劑；與萃取蒸餾系統相比，透過此複合程序，在最佳的溶劑流量之下，再沸器熱負載可大幅減少64.09%。再者，同時考慮開環路與閉環路敏感度測試的結果下，本研究提出一種創新的控制架構，藉由一個在動態控制期間可調動的溶劑流量，可允許程序操作在最適化的穩態點，而動態模擬結果顯示無論在新鮮進料流量或組成發生巨大改變之下，正丙醇與水產物皆能維持在高純度。
This work is divided into two parts. One is the separation of a mixture including methyl methacrylate, methanol, and water. The other is the investigation into hybrid extraction−distillation process with a case study of n-propanol dehydration. In the first part, an energy-saving design for the separation of a mixture including methyl methacrylate, methanol, and water is investigated as compared to a previous two-column design using the same process units but different configurations. In this energy-saving design, top and bottoms products of the regular distillation column are designed to be at unstable and stable nodes, respectively. Thus, results show that significant savings in the steam cost (16.3%) can be realized as opposed to the previous design of placing the bottom product at a saddle point. Another benefit is that the loss of methyl methacrylate product through the water outlet stream is also less than that of the previous design, representing another 9.6% savings of the operating cost for this energy-saving design. Furthermore, an overall control structure for this proposed design is also devised based on a novel way of using open-loop and closed-loop sensitivity tests. By the control of a temperature difference at two trays of the regular distillation column and another single-tray temperature at the stripper, both MMA and water products can be maintained at high purities despite large variations in feed flow rate and feed composition changes. In the second part, hybrid extraction−distillation separation system, which is a process combining the techniques of liquid-liquid separation and also distillation, is well investigated. This hybrid system can be viewed as a derivative from heterogeneous azeotropic distillation method. In this work, the potential for significant energy-saving via this hybrid process is demonstrated with both conceptual illustration and a case study of n-propanol dehydration. Diisopropyl ether (DIPE) is selected as the extraction solvent considering its favorable properties of density, heat of vaporization, and less toxicity. With the optimized solvent flow rate via this process, significant saving on reboiler duty (64.09%) can be realized compared to an extractive distillation system. Furthermore, a novel control strategy is proposed based on closed-loop and open-loop sensitivity tests. Here, an adjustable solvent flow rate during dynamic control allows the operation at the optimal steady-state condition. Dynamic simulation results show that both n-propanol and water products can still be maintained at high-purities despite large variations in feed flow rate and feed composition changes.
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