在連續操作的化學工廠運行中難免會發生不可預期的意外，可能會造成大量的原物料浪費及嚴重的環境危害，因此在本研究中藉由過去操作經驗及Aspen Plus Dynamics ®軟體模擬的輔助，預先制定發生特定意外事件後的緊急應變步驟。
具體而言，本研究探討乙烯工廠前端單元(如壓縮機)故障後，造成下游串連蒸餾塔分離系統的進料中斷，須等待前端故障排除後再恢復分離操作的緊急應變操作策略，由過去的經驗可知其中包括(1)停俥再開(2)文獻中提及所謂「追尾(tailchase)」(Chenevert et al., 2005)的操作(3)全回流，追尾操作細節為將下游出料再循環至進口處使該部分蒸餾系統仍可以持續運行，並在進料恢復時可以迅速地還原到初始穩態操作。本研究具體的工作有: (1) 建立穩態系統的質能平衡；(2) 將系統初始化並根據前述策略建立操作步驟；(3) 將操作步驟整理成順序功能圖(SFC)，並利用Aspen Plus Dynamics ® 進行不同參數下的動態模擬，驗證並評估各步驟的可行性；(4) 量化比較各操作步驟的優劣。我們最後發現，將追尾法及全迴流應用於上游進料中斷時間不長的情境下，串連蒸餾塔分離系統的緊急應變操作可以減少大量廢料，並縮短操作時間。但由於追尾及全迴流操作在等待進料恢復期間會持續產生能耗，因此在長時間上游進料中斷情況下，仍應採用停俥再開的方法，可以減少持續的能源損耗。

In operating a realistic chemical plant, it is very difficult to mitigate or even prevent accidents occurring online. Almost every abnormal event may end up with harmful outcomes, such as raw material losses, equipment damages, human injuries, and disastrous effects on the ecosystems, etc. Although the real-time data of unexpected incidents are extremely rare, there is still a pressing need to generate the emergency response procedure in advance to counteract every imaginable accident that results in undesired consequences. It is thus the objective of the present study to address this procedure-synthesis issue with the help of similar prior operational experiences and simulation results produced with commercial software, e.g., Aspen Plus Dynamics ®. Obviously, carrying out the simulation studies is obviously advantageous since this practice enables us to assess the impacts of any arbitrarily selected operation step without the risk of driving the actual system into a dangerous state. Although such an approach may not be ideal, the resulting procedure should at least be feasible in realistic industrial environment and could be used as the basis for further improvements.
Various possible incidents in an ethylene plant (or any other process) can be used as worked examples to illustrate the proposed procedure-generation method for emergency response. Due to space limitation, only one of them is studied in this thesis, that is, the synthesis task of conjecturing a suitable action sequence after the unexpected event of compressor breakdown. On the basis of the operational experiences in plant startup/shutdown, Chenevert et al. (2005) and other professional engineers brought up the ideas of replacing the original separation system configuration with two revised ones, i.e., tail chase and total reflux. This practice was based on the argument that, although the overhead gas streams should inevitably be off spec under unsteady conditions, the above-mentioned two configurations can be adopted to route them back to the distillation columns rather than sending them directly to the flare stack that causes significant green-house gas emission. On the other hand, an extra advantage of adopting either one of the aforementioned two system configurations and the corresponding response operations is the ability to keep the distillation train running continuously during the time period needed for compressor repair. This is because, in addition to avoiding material loss vented through the flare stack, it is also desirable to return to the original steady state as quickly as possible after the inputs to the separation system resume.
Specifically, the required design tasks can be summarized as follows: (1) perform steady-state modeling for laying down the foundation of dynamic simulation; (2) initialize the system and then establish various sequences of operating steps according to the aforementioned procedure-synthesis strategies; (3) summarize every procedure with a sequential function chart (SFC) and confirm its feasibility with Aspen Plus Dynamics ® (4) compare the pros and cons of all operating procedures constructed in the previous three tasks. It can be observed that the two proposed response strategies shorten operation time considerably and also achieve material and energy savings if the feed interruption is only temporary. However, since the tail chase and total reflux operations both consume energy continuously, should a long-term upstream feed interruption be anticipated, it may be more beneficial to use the traditional method of carrying out first the shutdown and then the startup operations separately during two distinct time intervals.

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