改善三塔真空變壓吸附程序捕獲煙道氣中二氧化碳之實驗設計分析

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Title:	改善三塔真空變壓吸附程序捕獲煙道氣中二氧化碳之實驗設計分析
Authors:	魏子倫;Wei, Tzu-Lun
Contributors:	化學工程與材料工程學系
Keywords:	真空變壓吸附;二氧化碳;煙道氣
Date:	2020-08-20
Issue Date:	2020-09-02 15:18:39 (UTC+8)
Publisher:	國立中央大學
Abstract:	近年來，為了減少二氧化碳排放量以減緩全球暖化現象，碳捕獲與封存(Carbon Capture and Storage，簡稱CCS）的相關技術扮演了重要的角色。在眾多碳捕獲方法中，變壓吸附程序因具有低能耗、低操作成本與簡單操作等優點而逐漸備受重視，其原理主要是藉由吸附劑對於混合氣體選擇性高低的不同，以及吸附劑在低壓時利於脫附、高壓時利於吸附之特性，來達到氣體分離的目的。本實驗以EIKME 13X分子篩作為吸附劑搭配三塔九步驟真空變壓吸附程序捕獲燃煤發電廠排放後經預處理之煙道氣中二氧化碳，預處理後之煙道氣進料含有的二氧化碳濃度約為9.00% ~ 11.74%。為了獲得能讓二氧化碳純度達90%以上，回收率達80%以上的操作設定，本研究選擇三塔九步驟程序中的步驟1/4/7時間(壓力平衡/逆向減壓時間)、步驟2/5/8時間(高壓吸附/壓力平衡時間)和步驟3/6/9時間(高壓吸附/同向減壓時間)做為變因建立2水準3因子之全因子設計(full factorial design)，總共需進行8組實驗，實驗結果可以用於探討各因子對二氧化碳純度、二氧化碳回收率及真空幫浦能耗的影響，接著利用複迴歸分析法(multiple regression analysis)分別建立二氧化碳純度、二氧化碳回收率、真空幫浦能耗的迴歸模型，最後將二氧化碳純度、二氧化碳回收率、真空幫浦能耗的迴歸模型共同進行最適化，預期達到二氧化碳純度90%以上、二氧化碳回收率80%以上的結果，並可推估此結果下的因子設定。由因子顯著性的相關分析結果可得知，對二氧化碳純度具有顯著效應的因子為步驟3/6/9時間(高壓吸附/同向減壓時間)，對二氧化碳回收率而言則為步驟1/4/7時間(壓力平衡/逆向減壓時間)和步驟3/6/9時間(高壓吸附/同向減壓時間)；而真空幫浦能耗則沒有任何因子對其有顯著的影響效應。透過Minitab軟體針對二氧化碳純度、二氧化碳回收率與真空幫浦能耗的迴歸模型共同進行最適化的結果為二氧化碳純度最高值達92.08%，二氧化碳回收率最高值達84.32%，真空幫浦能耗最低值達2.22 GJ/tonne CO2，若對比8組實驗結果可發現第2組的實驗結果，二氧化碳純度92.01%、二氧化碳回收率84.18%、真空幫浦能耗2.20 GJ/tonne CO2，與最適化計算結果非常接近，由此可知模型具有一定程度的預測性與準確度；另外，最適化所推估出的變因設定即為本次實驗的最佳操作條件，而該設定與第2組實驗之操作條件完全相同，均為步驟1/4/7時間(壓力平衡/逆向減壓時間)：400秒、步驟2/5/8時間(高壓吸附/壓力平衡時間)：200秒、步驟3/6/9時間(高壓吸附/同向減壓時間)：90秒。 ;In order to reduce the emission of carbon dioxide (CO2) to mitigate global warming, carbon capture and storage (CCS) technology plays an important role in recent years. Among of the methods for carbon dioxide capturing, pressure swing adsorption process (PSA) has obtained more attention, which is characterized by advantages such as low energy consumption, low investment, and simple operation. Based on the various selectivities of gas mixtures toward adsorbent, and according to the properties of adsorption at high pressure and desorption at low pressure, PSA uses these principles to achieve the target of gas separation. This study utilized EIKME 13X zeolite as adsorbent with a 3-bed 9-step VPSA process to capture CO2 from pretreated flue gas exhausted by a coal-fired power plant. The CO2 concentration of pretreated flue gas is about 9.00% ~ 11.74%. To reach the goals of CO2 purity above 90% and CO2 recovery above 80%, this research chose pressure equilization / countercurrent depressurization time, adsorption / pressure equilization time and adsorption / cocurrent depressurization time of 3-bed-9-step VPSA process as the factors to set up two-level three-factor full factorial design. There were 8 experiments to be conducted. The results of experiments were used to investigate the effect of factors on CO2 purity, CO2 recovery and energy consumption of two vacuum pumps. Next, the multiple regression analysis method was utilized to build regression models of CO2 purity, CO2 recovery and energy consumption of two vacuum pumps, respectively. Finally, the regression models of CO2 purity, CO2 recovery and energy consumption of two vacuum pumps were optimized by Minitab software with CO2 purity and CO2 recovery expecting to reach above 90% and 80%, and the factors setting were estimated under this condition. From the analyzed results, the factor adsorption / cocurrent depressurization time is the significant effect for CO2 purity; the factors pressure equilization / countercurrent depressurization time and adsorption / cocurrent depressurization time are the significant effects for CO2 recovery; there is no factor significant for energy consumption of vacuum pumps. The results of optimizing CO2 purity, CO2 recovery and energy consumption of two vacuum pumps regression models show optimal CO2 purity 92.08%, CO2 recovery 84.32% and energy consumption of vacuum pumps 2.22 GJ/tonne CO2. Comparing with 8 experiments, the optimization results are nearly the same as the second experiment results : CO2 purity 92.01%, CO2 recovery 84.18% and energy consumption of vacuum pumps 2.20 GJ/tonne CO2. Namely, the regression models present very good predictability and accuracy. On the other hand, the factors found from optimization results are the best operating conditions of this research, and those factors are as same as the operating parameters of the second experiment. The best operating parameters are listed as the follows : pressure equilization / countercurrent depressurization time 400 seconds, adsorption / pressure equilization time 200 seconds, and adsorption / cocurrent depressurization time 90 seconds.
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