| 摘要: | 2021年政府規劃將燃氣發電占比拉高至五成，相較燃煤發電，燃氣發電可大幅減少很多空汙物排放，為減少空汙、提升國內空氣品質等，政府規劃能源政策，希望在2025年，能達到將電力結構調整為低碳天然氣發電占比50%，並將燃煤發電占比降至30%，再生能源發電量則要成長達20%，因此天然氣廠燃燒後的二氧化碳也逐漸受到重視。
為了減少化石燃料燃燒排放碳排二氧化碳至大氣中，造成溫室效應的惡化，因此捕獲燃燒後煙道氣中二氧化碳為一重要技術，在眾多碳捕獲方法中，變壓吸附法是常用的一種連續性循環程序氣體吸附分離技術，根據吸附劑對於混合氣體選擇性高低的不同，以及高壓時利於吸附劑吸附、低壓利於脫附之特性，進行高低壓循環程序達到氣體分離的目的，其因具有低能耗、低操作成本與容易操作等優點而逐漸備受重視。
本研究以雙塔六步驟變壓吸附法捕獲天然氣電廠所排放之煙道氣中二氧化碳為目的，以5%二氧化碳與95%氮氣作為進料，並選用UOP 13X作為本研究所使用之吸附劑，將之填入吸附塔內進行突破及脫附曲線實驗，藉由改變不同的進料壓力與溫度，觀察其對突破曲線及脫附曲線之影響，並以此參數作為設計基礎，進行後續雙塔變壓吸附程序模擬之依據。
研究中首先藉由單塔三步驟程序實驗與模擬結果進行驗證，確認模擬程式的可信度。接著透過高壓吸附、壓力平衡、同向減壓、逆向減壓之變壓吸附雙塔六步驟與單塔三步驟二階段變壓吸附程序模擬，探討塔底二氧化碳純度及回收率變化。利用第一階段雙塔六步驟和第二階段單塔三步驟變壓吸附程序找到基礎條件，達到塔底產物二氧化碳純度33.18% 和回收率82.75%。
為了有效找出最佳操作條件，利用實驗設計(Design of Experiments, DOE)，針對各操作變因進料壓力、進料溫度、抽真空壓力、進料加壓/逆相減壓時間及高壓吸附/同相減壓時間作為操作變因，探討塔底二氧化碳純度及回收率變化，其顯示出最適化所需之操作條件，為進料壓力3.45 atm、進料溫度338K、抽真空壓力0.15 atm、步驟1/4時間20秒和步驟3/6時間30秒的雙塔六步驟程序條件下，能得到塔底產物二氧化碳純度45.35 %及回收率93.32%，能耗為5.31 GJ/t-CO2的最適化結果。接著透過第一階段塔底產物進入第二階段單塔三步驟提高塔底二氧化碳純度，達到塔底產物二氧化碳純度94.83 %及回收率95.20 %，能耗為1.23 GJ/t-CO2，整體回收率為88.84%，整體能耗為6.81 GJ/t-CO2。
;In 2021, the government plans to increase the proportion of gas-fired power generation to 50%. Compared to coal-fired power generation, Gas-fired power generation can significantly reduce a lot of air pollution emissions. Government plans energy policy to reduce air pollution and to improve domestic air quality. It wishes to adjust the power structure to low-carbon natural gas power generation accounted for 50% , to reduce the proportion of coal-fired power generation to 30%, and renewable energy power generation will reach by 20% in 2025.Therefore, the carbon dioxide emitted from natural gas power plant has gradually received attention.
In order to mitigate the effects of global warming and reduce emissions, we use pressure swing adsorption process to capture carbon dioxide from flue gas in a natural gas power plant. Among the methods for carbon dioxide capturing, pressure swing adsorption (PSA) is a cyclic process to separate gas mixtures based on the difference of adsorption capacity of each component on adsorbent, and based on the properties of adsorption at high pressure and desorption at low pressure, PSA uses these characteristics to achieve the target of gas separation, and pressure swing adsorption process (PSA) has obtained more attention, which is characterized by advantages such as low energy consumption, low investment, and simple operation.
This work presents a study for capturing carbon dioxide from simulate dry flue gas (5% CO2 / 95% N2) emitted from a natural gas power plant using UOP 13X as adsorbent.The breakthrough and desorption curves were discussed by changing different feed pressure and temperature,and results were used to conduct the design of experiment of dual-bed PSA process.
Then, the simulation is verified with experiments of a single-bed PSA process.A two stage PSA process is studied to capture CO2 from flue gas of natural gas power plant.The first stage 2-bed 6-step PSA process is used with adsorption, pressure equalization, cocurrent depressurization and countercurrent depressurization steps and the second stage 1-bed 3-step PSA process is used with adsorption, cocurrent depressurization and vacuum steps to separate flue gas with simulation.
In order to find the optimal operating conditions, this study combined the simulation of the first-stage 2-bed 6-step PSA process with design of experiments (DOE) method. Parameter study was implemented to obtain a series of optimized settings of operating variables by investigating the effects of feed pressure, feed temperature, vacuum pressure, pressurization/ countercurrent depressurization time, adsorption/ cocurrent depressurization time. After simulation analysis, the bottom product CO2 purity is 45.35 % with 93.32 % recovery while at feed pressure 3.45 atm, feed temperature 338K, vacuum pressure 0.15 atm, step 1/4 time 20 s, and step 3/6 time 30 s as the optimal results. The mechanical energy consumption was estimated to be 5.31 GJ/t-CO2. Then the purity of carbon dioxide obtained from the second-stage 1-bed 3-step PSA process. The bottom product CO2 purity is 94.83 % with 95.20 % recovery, which makes a total recovery of 88.84% .The energy of the second stage PSA is 1.23 GJ/t-CO2, which makes a total energy consumption of 6.81% |
