以變壓吸附法捕獲發電廠煙道氣中二氧化碳之模擬研究與實驗設計分析

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Title:	以變壓吸附法捕獲發電廠煙道氣中二氧化碳之模擬研究與實驗設計分析
Authors:	鄭筑勻;Cheng, Chu-Yun
Contributors:	化學工程與材料工程學系
Keywords:	變壓吸附;二氧化碳捕獲;燃燒後捕獲;實驗設計分析;Pressure Swing Adsorption;CO2 capture;Post-combustion;Design of Experiments Analysis
Date:	2019-08-19
Issue Date:	2019-09-03 12:33:41 (UTC+8)
Publisher:	國立中央大學
Abstract:	為了減少二氧化碳的排放量，可利用變壓吸附法捕獲煙道氣中二氧化碳，變壓吸附法為一種連續性循環程序氣體吸附分離技術，利用吸附劑對氣體混合物中各成分之不同吸附選擇性來分離氣體，具有低能耗、低操作成本與簡單操作等優點，本研究目的為捕獲燃煤及燃氣電廠1kW等級煙道氣中二氧化碳，使得塔底產物二氧化碳達到純度85%以上及塔頂氮氣90%以上。第一步以實驗數據中各氣體成份CO2、N2對吸附劑的平衡吸附量進行迴歸得到等溫吸附模型所需參數後，選用線性驅動力質傳模式(Linear Driving Force model, LDF)，藉由突破曲線實驗及脫附實驗驗證理論計算具有相當高的可信度，並利用三塔九步驟程序捕獲電廠煙道氣100小時穩態實驗與模擬結果進行驗證，更加一步確認模擬程式的準確性。將研究內容分為兩部分，皆選用EIKME 13X沸石為吸附劑。第一部份利用三塔九步驟變壓吸附系統，以1kW等級亞臨界燃煤鍋爐煙道氣，經除硫、除水後之13.5%二氧化碳與86.5%氮氣為進料，進料流量為60.00 L/min (NTP)，得到在進料壓力3 atm，進料溫度303.14K，抽真空壓力0.07 atm，同向減壓壓力0.25 atm吸附時間430秒，同向減壓時間80秒，抽真空時間300秒，壓力平衡時間50秒，塔底產物二氧化碳純度為85.96 %，回收率82.09 %，塔頂產物氮氣純度為97.61 %，回收率92.05%，能耗為1.06-1.24 GJ/tonne-CO2。為了有效找出最佳操作條件，利用實驗設計(Design of Experiment, DOE)，結合變異數分析(Analysis of Variance, ANOVA)和反應曲面法(Response Surface Methodology, RSM)二階模型，進行中央合成設計實驗(Central Composite Design, CCD)，並結合迴歸分析計算出純度極大值、回收率極大值、能耗極小值、最適化所需之操作條件，當進料壓力3.66 atm、抽真空壓力0.05 atm、同向減壓壓力0.3 atm、環境溫度323.14 K、步驟1/4/7時間94秒、步驟2/5/8時間350秒、塔長46公分的操作條件下，能得到塔底產物二氧化碳純度89.20 %，回收率88.20%，塔頂產物氮氣純度98.49 %，回收率93.56 %，能耗為1.17-1.41 GJ/tonne CO2的最適化結果。第二部分探討1kW等級燃氣電廠煙道氣，經除硫、除水後之5%二氧化碳與95%氮氣，利用三塔九步驟變壓吸附程序進行模擬，得到在進料壓力4 atm，進料溫度303.14K，抽真空壓力0.05 atm，同向減壓壓力0.2 atm，吸附時間620秒，同向減壓時間120秒，抽真空時間450秒，壓力平衡時間50秒，進料流量132.59 L/min (NTP)的操作條件下，得到塔底產物二氧化碳純度為86.31 %，回收率65.50 %，塔頂產物氮氣純度為98.36%，回收率96.83 %，能耗為4.03-4.93 GJ/tonne-CO2。 ;In order to reduce carbon dioxide emissions, we use pressure swing adsorption process to capture carbon dioxide from flue gas in a thermal power plan . Pressure swing adsorption (PSA) is a cyclic process to separate gas mixtures based on the difference of adsorption capacity of each component on adsorbent. Pressure swing adsorption plays an important role in the separation of gas mixtures with its low energy consumption, low investment, and simple operation. This study aims to capture carbon dioxide from flue gas of 1kW coal-fired and gas-fired power plant by PSA process for bottom product CO2 purity 85% and top product N2 purity 90%. To validate the accuracy of PSA program, the extended Langmuir-Freundlich equation was adopted to fit isotherm to describe the adsorption equilibrium of adsorbent. Next, we used linear driving force (LDF) model and compared the results of breakthrough curves and desorption curves between experiments and simulation to verify the accuracy of mass transfer coefficient kLDF value. We further verified the simulation with the 100 hours steady state experiment of 3-bed 9-step PSA process . Next, this study could be divided into 2 parts and both of them used EIKME 13X zeolite as adorbent. For the first part of study, a 3-bed 9-step pressure swing adsorption (PSA) process for flue gas after desulphurization and water removal (13.5 % CO2, 86.5% N2) of subcritical 1kW- coal-fired power plant was designed. After simulation, we obtained a bottom product CO2 purity at 85.96% with 82.09% recovery, and a top product N2 purity at 97.61 % with 92.05% recovery while at feed flow rate 60 L/min (NTP), feed pressure 3 atm, vacuum pressure 0.05 atm, feed temperature 303.14 K, adsorption time 430 s, cocurrent time 80 s, vacuum time 300 s, and pressurization equilibrium time 50 s. The mechanical energy consumption was estimated to be 1.06-1.24 GJ/tonne-CO2. In order to find the optimal operating conditions, we combined the results of 1kW-power plant flue gas PSA process with design of experiments (DOE) method. After analysis, we obtained a bottom product CO2 purity at 89.20% with 88.20% recovery, and a top product N2 purity at 98.49 % with 93.56 % recovery while at feed pressure 3.66 atm, vacuum pressure 0.05 atm, cocurrent depressurization 0.3 atm , surrounding temperature 323.14 K, step 1/4/7 time 94 s, step 2/5/8 time 350 s, bed length 46cm as the optimal results. The mechanical energy consumption was estimated to be 1.17-1.41 GJ/tonne-CO2. For the second part of study, we use same process for capturing CO2 from flue gas of a power plant with natural gas as fuel. The composition of flue gas was assumed 5% CO2 and 95% N2 .After simulation, we obtained a bottom product CO2 purity at 86.31 % with 65.50 % recovery , and a top product N2 purity at 98.36% with 96.83 % recovery while at feed flow rate 132.59 L/min (NTP), feed pressure 4 atm, vacuum pressure 0.05 atm, cocurrent depressurization pressure 0.2 atm, feed temperature 303.14 K, adsorption time 620 s, cocurrent time 120 s, vacuum time 450 s, and pressurization equilibrium time 50 s. The mechanical energy consumption was estimated to be 4.03-4.93 GJ/tonne-CO2.
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