利用三塔式真空變壓吸附法捕獲燃煤電廠煙道氣中二氧化碳之實驗研究

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Title:	利用三塔式真空變壓吸附法捕獲燃煤電廠煙道氣中二氧化碳之實驗研究
Authors:	郭家禎;Kuo, Chia-Chen
Contributors:	化學工程與材料工程學系
Keywords:	真空變壓吸附;捕獲二氧化碳;煙道氣;燃煤電廠;13X 沸石;Vacuum pressure swing adsorption;Capture carbon dioxide;Flue gas;Coal-fired power plant;Zeolite 13X
Date:	2020-01-20
Issue Date:	2020-06-05 17:04:10 (UTC+8)
Publisher:	國立中央大學
Abstract:	近年來，大多數工業國家已經意識到溫室氣體，特別是大量排放的二氧化碳對環境的重要影響。人們普遍認為溫室氣體逐年升高是地球年平均溫度升高的主要原因。對於這個嚴重的問題，許多國家提倡碳捕集、封存和再利用技術（Carbon Capture,Storage and Utilization,CCSU）以減少二氧化碳的排放。為了捕獲二氧化碳，變壓吸附法（Pressure Swing Adsorption, PSA）是一種具有能耗低、投資少、操作過程簡單等特點的氣體分離方法。本研究為燃煤電廠預處理後的煙道氣提供了一種真空變壓吸附程序(Vacuum Pressure Swing Adsorption, VPSA)捕獲二氧化碳的方法，其目的在長時間(100小時)的運轉下，其產物二氧化碳純度達到85%以上。我們選擇沸石13X分子篩作為吸附劑，使用Thermo Cahn D-200 Digital Recording Balance在不同溫度下量測CO2和N2等溫吸附曲線，以描述吸附平衡的行為，並將吸附劑放入吸附塔中以不同進料濃度與流量進行突破實驗，討論進料濃度與流量對於吸附塔與突破時間的影響。研究中採用三塔九步驟VPSA程序並使用小型吸附床其直徑和高分別為0.16 m和0.6 m從燃煤電廠煙氣中捕獲CO2，基本操作條件為進料壓力3.2 bar、同向減壓的壓力為0.4 bar與真空壓力為0.1 bar。實驗研究結果顯示，在第280個循環時，塔底產物的CO2純度為與回收率分別為91.01%與58.46％，總機械能耗包含洗滌塔的抽水馬達、吸附式壓縮空氣乾燥機、加壓泵浦、同向減壓的真空泵浦及逆向減壓的真空泵浦為7.89 GJ /tonneCO2，其中真空泵浦的能耗只佔了1.39 GJ /tonneCO2。並在長時間(100小時)的運轉操作中每24小時從吸附塔內取出部分的吸附劑，量測其吸附能力隨時間的變化。然後我們利用純CO2與N2做適當的控制混合出5% CO2 + 95% N2與20% CO2 + 80% N2的進料氣體濃度，在相同的3塔9步驟的操作程序下可分別獲得塔底產物純度為50.28% 與96.42%，我們並針對不同濃度的進料氣體作程序時間的修改，改善其塔底產物二氧化碳的純度或回收率：進料為煙道氣時，其塔底產物二氧化碳純度從92.04%下降至82.26%，回收率從59.01%上升至60.58%，及機械能耗從7.64 GJ /tonne CO2 下降至 7.56 GJ /tonne CO2；進料為5%CO2+95%N2混合氣時，其塔底產物二氧化碳純度從50.28%上升至82.89%，回收率從49.04%下降至40.24%，及機械能耗從5.09 GJ /tonne CO2 上升至5.31 GJ /tonne CO2；進料為 20%CO2+80%N2混合氣時，其塔底產物二氧化碳純度從96.42%下降至96.09%，回收率從48.33%上升至50.31%，及機械能耗從1.54 GJ /tonne CO2 下降至 1.48 GJ /tonne CO2。 ;In recent years, most industrial countries come to realize the important environmental effect by greenhouse gas, especially massively discharged carbon dioxide. The greenhouse gas was generally recognized the main cause of annual average temperature rise on earth year by year. For this serious issue, many countries promote carbon capture, storage and utilization (CCSU) to lower the carbon dioxide emission. In order to capture carbon dioxide, pressure swing adsorption (PSA) is one of gas separation methods which features low energy consumption, lower capital investment, and simple operating process. This study provides a vacuum pressure swing adsorption process for the capture of carbon dioxide for pretreated flue gas from coal-fired power plants. The research purpose is to get the bottom product with a carbon dioxide purity of over 85% for a long time (100 hours) operation. We selected zeolite 13X molecular sieve as the adsorbent, used Thermo Cahn D-200 Digital Recording Balance to measure the isotherm of CO2 and N2 at different temperatures to describe the behavior of adsorption equilibrium. Then we put the adsorbent into the adsorption bed to do the breakthrough experiments with different feed concentration and flow rate, and discussed the effects of feed concentration and flow rate on adsorption bed and breakthrough time. In this study, a 3-bed-9-step VPSA process was utilized to capture CO2 from the flue gas of the coal-fired power plant with a bench-scale adsorption bed of 0.16 m diameter and 0.6 m length and the basic operating circumstance was set at feed pressure 3.2 bar, cocurrent depressurization pressure 0.4 bar, and vacuum pressure 0.1 bar. The experimental study showed a result of bottom product with 91.01 % purity and 58.46 % recovery of CO2, and the total mechanical energy consumption including water pumping motor of the scrubber, air dryer, air compressor, and two vacuum pumps for cocuurrent and countercurrent depressurization was 7.89 GJ / tonne CO2 for the 280th cycle, and two vacuum pumps only accounted for 1.39 GJ / tonne CO2. We also took out some particles of the adsorbent from the adsorption bed every 24 hours during long time (100 hours) operation and measured the change of its adsorption capacity with time. Then we used pure CO2 and N2 to make appropriate control to mix 5% CO2 + 95% N2 and 20% CO2 + 80% N2 as feed concentration and the bottom product could be obtained 50.28% and 96.42% under the same 3-bed-9-step operation process. The operation time was modified for different feed concentration to improve the CO2 purity or recovery of the bottom product. When the feed was the flue gas, the purity of the bottom product dropped from 92.04% to 82.26%, the recovery increased from 59.01% to 60.58%, and the mechanical energy consumption decreased from 7.64 to 7.56 GJ /tonne CO2. When feed was 5% CO2 + 95% N2, the purity of the bottom product increased from 50.28% to 82.89%, the recovery decreased from 49.04% to 40.24%, and the mechanical energy consumption increased from 5.09 to 5.31 GJ /tonne CO2. When feed was 20% CO2 + 80% N2, the purity of the bottom product decreased from 96.42% to 96.09% a, the recovery increase from 48.33% to 50.31%, and the mechanical energy consumption decreased from 1.54 to 1.48 GJ /tonne CO2.
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