內隔壁式蒸餾塔之穩態設計與經濟效應分析

Abstract

相較於傳統的蒸餾序列，內隔壁式蒸餾塔（DWC）可以節省更多的能量與與設備成本。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。此研究針對三種型態之內隔壁式蒸餾塔提出一套捷徑式設計法，在此我們建立了一個合理且有效率的物質流模組來描述塔內的物質流動，此方法是建立在將塔結構分成數個區域，並且應用Fenske、Underwood、Gilliland和Kirkbride公式來計算各個區域的設計變數。兩種真實系統的嚴謹模擬被用來驗證此設計法的成效，結果顯示藉由此方法所得到之設計結果很接近最小年總成本之設計。並且此設計方法也可提供最適化之起始值。在經濟效應分析的部份，我們藉由此設計法來計算各種不同分離難度指標進料下之年總成本。最後，根據最小年總成本我們可以知道在不同進料條件之下該如何選用哪一種內隔壁式蒸餾塔的指標。然而，控制方面的問題也應該被探討，對於隔板在中間與在上方的兩種內隔壁式蒸餾塔而言，氣提的分流將會是一個擾動，而此問題不存在於隔板在下方型態的蒸餾塔，因為此一考量，若在年總成本相同的情況下，則建議選用隔板在下方型態之內隔壁式蒸餾塔。本研究提供了一套捷徑式設計法，在不同的進料條件下之經濟效應分析也在本研究中被介紹。

Divided-wall columns (DWCs) can save energy and capital cost compared with traditional distillation columns. However the design of DWCs is more difficult because there are more degrees of freedom. This work provides a novel shortcut method that can be used for the design of three types of DWCs. A rational and efficient net flow model is constructed to describe DWC systems. The development of the method is based on dividing the DWC into several parts and applying the methods of Fenske-Underwood-Gilliland and the Kirkbride equation. A series of rigorous simulations are applied to two real systems in order to show the performance. The results show that the total annual cost (TAC) based on the design method is close to the minimum total annual cost. This method also provides good initial values for rigorous optimization. In economic analysis, this method is applied to calculate the total annual cost for different Ease of Separation Index (ESI) and different feed composition for three types of DWCs. Finally, the criterion of the choice of DWCs is presented according to TAC. However the control aspect should also receive attention, because of the vapor split disturbance problem for DWCM and DWCU. For an equivalent TAC, it is suggested to use DWCL according to this operating consideration. The steady state design and economic analysis for three types of DWCs in different feed condition are investigated in this work.