| Abstract: | 本論文以模擬方式探討微蒸餾系統之性能。本研究在Aspen Custom ModelerR平台上，建立精餾段、氣提段、冷凝器與再沸器之數學模式，並探討系統之穩態特性、參數影響與阻力分析，且與傳統塔及中空纖維蒸餾塔進行比較。
在塔內特性分佈方面，微蒸餾塔之操作可獲較接近線性之溫度與組成分佈，亦即微蒸餾塔可較充分利用塔之硬體空間，因此其HTU僅需數公分。然而，其有效平衡曲線偏離於平衡曲線甚遠，不利於能源耗用之表現，可用能損耗分析也確認了此結果。此外，因氣液相無法直接接觸交流也導致氣、液通道內分別會有少量液相與氣相之存在。
在參數影響分析方面，結果顯示，對於產物純度之影響以再沸比、迴流比和薄膜厚度較其他條件明顯，而對於塔之熱負荷量而言，則以系統進料流量和薄膜孔徑有較明顯之影響。
阻力分析方面，發現質傳係數對產物純度和熱負荷量之影響比熱傳係數大，且因質傳阻力主要落在液相，故微蒸餾塔性能提升之關鍵即在於液體通道質傳係數之改善。
微蒸餾塔與傳統塔之比較部份，在達到相同產物純度條件下，HTU僅需數公分，大幅優於傳統塔之數十公分，主要質傳阻力分別在於液相與氣相，也是重要差異。微蒸餾塔與中空纖維蒸餾塔之性能則較接近，例如HTU與單位體積之介面面積，然而質傳阻力之分佈特性則不一致，微蒸餾塔之總質傳係數較高，且薄膜層阻力相對不重要，中空纖維塔之薄膜層阻力則為最主要阻力或與液相阻力相當。
This thesis investigates the performance of micro distillation columns (MDC) by simulation study. The mathematical models of the rectifying section, stripping section, condenser and reboiler are built on the Aspen Custom Modeler R platform. The steady state characteristics of the distillation system, parametric study of operating and device variables, heat and mass transfer resistances are analyzed. The micro distillation column, conventional distillation columns (CC) and hollow fiber distillation columns (HFC) are compared for their transfer characteristics and separation performance.
On the internal profiles of the micro distillation column, the operation gives close to linear temperature and composition distributions, indicating more effective utilization of the column space and leads to a HTU (height of a transfer unit) of only a few centimeters. However, the effective equilibrium curve significantly deviates from the equilibrium curve, which is not beneficial to the energy utilization. The exergy analysis confirms this result.
On the parameters influence study, the boilup ratio, reflux ratio and membrane thickness are the most significant factors affecting the product purity. For heat duties of the column, feed rata and membrane pore size give greater influence. The resistance analysis reveal that mass transfer resistance is much important than heat transfer resistance, in particular the liquid phase resistance. The improvement of the column should be focused on the mass transfer coefficient of the liquid channels.
To achieve the same product purity, the HTUs of MDC and CC are a few centimeters and tens of centimeters. The key mass transfer resistances of MDC and CC lie in the liquid phase and vapor phase, respectively. The characteristics of MDC and HFC are similar, such as the HTU and interface area per unit volume, but the distributions of mass transfer resistance are quite different. For MDC, the overall mass transfer coefficient is greater and the membrane resistance is not significant, however, the major resistance of HFC is on the membrane and liquid phase. |
