內隔壁式蒸餾塔之動態與控制

Abstract

相較於傳統的蒸餾序列，內隔壁式蒸餾塔 (DWC) 是一種在分離多成分混合物時，可以節省更多的能量與設備成本的前瞻性設計。然而，內隔壁式蒸餾塔在設計上也較為困難，因為較傳統序列擁有更多的設計自由度。約莫五十年前，內隔壁式蒸餾塔的設計方法被提出討論，許多論文討論穩態設計問題，並提出啟發式和嚴謹的設計優化方法。但是，內隔壁式蒸餾塔的控制相對的得到較少的關注。此研究主要是針對內隔壁式蒸餾塔分離理想系統的可控性進行調查。對於不同類型的內隔壁式蒸餾塔、不同相對揮發度的分離指標、不同的進料條件，進行可控性的分析。並對於不同的控制策略，採用線性分析工具，相對增益陣列 (RGA) 和條件數 (CN) 進行分析。論文中為符合實際工廠使用的控制策略，利用進料擾動從動態上測試其排除干擾的能力。最後，從控制的角度提出一選擇何種類型內隔壁式蒸餾塔之指導方針。 從控制的觀點發現，當進料含有較多輕成分時建議使用上隔板式蒸餾塔；當進料含有較多中間成分時建議使用下隔板式蒸餾塔；當進料含有較多重成分時建議使用上隔板式蒸餾塔。

The divided-wall column system is a promising energy saving alternative for separating multi-component mixtures compared with traditional distillation columns. However the design of DWCs is more difficult because there are more degrees of freedom. The control of the DWC have received much less attention. In this work, the controllability of a divided wall column for separating ideal system were investigated. The main objective of this work is to study the divided-wall column (DWC) controllability. A controllability analysis of the ideal system is done for the separation of different types of DWC, different ease separation index (ESI) and different feed condition. Different control structures are compared using linear analysis tools, relative gain array (RGA) and condition number (CN). Disturbances in feed fowrate and feed composition are used to demonstrate the effectiveness of the proposed control structure. Finally, a guideline for the selection of the divided-wall column is proposed. Based on control considerations for different feed conditions, it is found that: If there is more lightest component in the feed, DWCU is preferred. If there is more middle component in the feed, DWCL is preferred. If there is more heaviest component in the feed, DWCU is preferred.