在現代化的化工製程中常會利用熱交換器網路（heat exchanger network, HEN）來回收廢熱。但在一般正常的操作情況下，在網路中每一熱交換器內隨時間產生的結垢現象是無法避免的，因此若沒有定期清洗，HEN就會無法達到原先預期的熱交換量。在過去研究中，Lavaja and Bagjewicz(2004)曾依據文獻中常用的結垢模式，建立出混整數非線性規劃(mixed-integer nonlinear programming, MINLP)模型，來決定出熱交換網路的最適清洗排程。雖然利用此一方式所得到的排程，可以有效降低因結垢導致熱回收不足所增加的額外公用流體成本，但清洗選定熱交換器的時期就必須停止原來製程所需熱交換工作，造成了額外公用流體的需求。因此本研究工作就是探討如何針對既有的熱交換網路配置備件，以便在清洗進行時取代無法提供服務的熱交換器。具體而言，我們修改傳統的MINLP模式的方法是引入了一組二元變數來代表在清洗時是否使用備件的選項，在相應最適解中，不但可決定清洗排程，還可決定備件總數、熱傳面積及使用時機。最後，在本論文中一系列的案例探討中也驗證了所提方法之可行性及有效性。

A well-designed heat-exchanger network (HEN) can often be adopted for maximum heat recovery in any modern chemical process. However, as time goes on under the normal operating conditions, fouling on the heat-exchange surface is unavoidable. If the heat-transfer units in a HEN are not cleaned regularly, the originally envisaged thermal efficiency can only be maintained for a short period of time.
Based on the published fouling models, Lavaja and Bagjewicz (2004) constructed a mixed-integer nonlinear program (MINLP) for synthesizing the optimal cleaning schedule of any given heat-exchanger network. Although this method could be used to produce schedules that effectively reduce the additional utility costs caused by fouling, the required cleaning operations still result in unnecessary utility consumption since the corresponding exchangers must be removed from duties.
The objective of this study is therefore to modify the aforementioned existing MINLP model so as to optimally assign spares to replace the units that are taken out of service for cleaning. Specifically, a set of binary variables are introduced and each is used to reflect whether a removed exchanger should be substituted with a spare. The corresponding optimal solution includes not only the cleaning schedule but also the total number of spares, their heat transfer areas and the substitution schedule. Finally, this thesis also provides the optimization results of a series of case studies to verify the feasibility and effectiveness of the proposed approach.

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