兩類近沸物分離之節能設計與控制

Abstract

本文探討各類近沸混合物系統的節能設計流程與控制，總共有兩組待分離的混合物：乙苯與苯乙烯系統及環己烷與環己烯系統。首先討論的近沸物質是乙苯與苯乙烯系統，本論文參考台灣某工廠的實際資料加以簡化為兩成分混合物後探討其分離段的節能設計流程，包括單一傳統蒸餾塔、多效熱整合蒸餾系統、內部熱整合蒸餾系統，其中單一傳統蒸餾塔是為基礎案例(Base case)與其他蒸餾系統比較。多效熱整合蒸餾系統中，探討了五種不同的設計架構，分別稱為Light-Split-Forward (LSF)、Light-Split-Reverse (LSR)、Heavy-Split-Forward (HSF)、Heavy-Split-Reverse (HSR)以及Feed-Split (FS)，其中以FS設計架構節省能源消耗的表現最為出色，也探討了此系統的動態控制架構。內部熱整合蒸餾系統相較於前述所有的設計架構節省了更多的能耗，但其設備成本較高，因此在設備攤還年限得以延長或是能源價格上漲的情況下優勢才會更加明顯。 本論文另外針對環己烷與環己烯分離系統，設計了一節省能源消耗的萃取蒸餾系統。環己烷與環己烯分離系統較上述乙苯與苯乙烯分離系統還要困難，其混合物間的相對揮發度更小，然而在適當的夾帶劑選擇之下，使用萃取蒸餾設計的方式能夠節省非常多的能源消耗。另外也透過簡單的熱整合方式，探討此流程進一步節能的可能性；此流程設計為常壓分離系統，因此也探討了壓力改變對於此流程的效益，將蒸餾塔操作在真空狀態下能夠更加降低能源消耗。

Energy-saving process design and control for the separation of some close-boiling mixtures will be discussed in this thesis. There are two systems including ethylbenzene/styrene and cyclohexane/cyclohexene will be investigated. For the separation of ethylbenzene and styrene, several designs including conventional distillation, multi-effect distillation and internally heat-integrated distillation column (HIDiC) are considered to save energy cost and total annual cost. Conventional distillation will be the base case in order to be compared with other distillation systems. For multi-effect distillation, five alternative configurations which include Light-Split-Forward (LSF)、Light-Split-Reverse (LSR)、Heavy-Split-Forward (HSF)、Heavy-Split-Reverse (HSR) and Feed-Split (FS), are studied. The results show that FS configuration can decrease most energy cost, so the dynamic control structure of this configuration is also investigated. HIDiC design can save more energy than any kind of multi-effect distillations but the capital cost is also higher so that this design will be economic favorable if payback period can be extended or the energy cost is increased. For the separation of cyclohexane and cyclohexene, some energy-saving designs of extractive distillation system are studied. Compared with ethylbenzene and styrene, this mixtures is harder to be separated because there relative volatility is much lower. The result shows that extractive distillation with suitable entrainer can save great amont of energy cost. Further more, simple heat-integrated design can decrease more energy cost. Energy consumption can be further reduced when columns are operated under vacuum condition.