| 摘要: | 第一部分:
生質沼氣平均成分為60~70%甲烷、30~40%二氧化碳、0~4000 ppm硫化氫及其他微量氣體等，然而甲烷與二氧化碳為溫室效應之主要氣體，其中，甲烷的全球暖化潛勢被估計為二氧化碳之28~36倍，對於溫室效應的影響力不容小覷。
本研究第一階段為三種商用吸附劑的選擇測試，包含13X沸石、5A沸石以及活性碳，針對每一種吸附劑分別進行甲烷及二氧化碳之等溫吸附曲線之實驗測量，並計算不同溫度下二氧化碳對甲烷的選擇率，做出各吸附劑之性能比較，選出13X沸石為較適用於變壓吸附法之吸附劑。第二階段根據第一階段中所選之分離性能最佳的吸附劑，以雙塔八步驟PSA程序進行沼氣純化系統設計，進料組成為核能研究所提供之經厭氧發酵的生質沼氣，其中包含64% 甲烷、36% 二氧化碳以及100 ppm 硫化氫。為了找出最佳的操作條件，本研究將雙塔八步驟PSA程序模擬與實驗設計(Design of experiments, DOE)方法相結合，最終可使塔頂產物甲烷純度達99.5%，甲烷回收率達91.3%，而 塔頂產物之硫化氫含量僅剩0.015 ppm，此產物可被注入於天然氣管網（>95% CH4）中，滿足天然氣管道中流體標準進而作為燃料使用，而程序中純化每噸甲烷產物所估計需要的能耗為0.86 GJ。
第二部分:
鑒於全球暖化日益嚴重，及再生能源發電中棄風棄光現象造成能源大量浪費的問題，因此電轉氣(Power to Gas, P2G)為目前歐盟所積極推動的儲能技術。此技術以電解水來產生氫氣，藉利用水電解產生的氫氣和二氧化碳進行甲烷化反應，為了使氫氣不被浪費，甲烷化反應中常會以二氧化碳過量的方式來進行，經反應後，產物組成為二氧化碳、甲烷及乙烷。為了後續的應用，本研究擬以變壓吸附程序(pressure swing adsorption, PSA)進行二氧化碳及甲烷分離之技術開發。
第一階段先依據文獻資料及吸附量實驗測量尋找至少兩種合適的商業吸附劑，經過二氧化碳對甲烷以及二氧化碳對乙烷的選擇率計算後，選出13X沸石為較適用於變壓吸附法之吸附劑。第二階段根據第一階段中所選之分離性能最佳的吸附劑，以雙塔八步驟PSA程序進行二氧化碳純化之PSA程序設計，以67.9%甲烷、30%二氧化碳及2.1%乙烷作為進料組成，最終可獲得塔頂出口甲烷純度為84.66%，回收率為95.53%，而塔底出口之二氧化碳純度為84.03%，Waste產物流的二氧化碳純度為91.30%，皆有到達純度目標值的70%以上，將此產物回收進行循環利用，以降低二氧化碳的排放量，達到提升碳循環效率。
;Part Ⅰ:
The average composition of biogas is 60-70% methane (CH4), 30-40% carbon dioxide (CO2), 0-4000 ppm hydrogen sulfide (H2S), and other trace gases. Both CH4 and CO2 emission are the causes of global warming. Furthermore, CH4 is estimated to have a global warming potential (GWP) of 28-36 over 100 years. Its influence on the greenhouse effect cannot be underestimated.
In the first part of study, PSA simulation program was applied to separate biogas. The adsorbent was chosen based on adsorption data from literature, Afterwards, we chose three commercial adsorbents to compare their performance, including activated carbon, zeolite 5A and zeolite 13X, and the sorbent parameters were calculated from experimental data of the adsorption equilibrium curve. We used 13X zeolite produced by COSMO as adsorbent due to its high CO2/CH4 selectivity. In the second part of study, a 2-bed 8-step PSA process is utilized to separate biogas (36% CO2, 64% CH4 and 100 ppm H2S) after desulphurization and water removal from the Institute of Nuclear Energy Research. After the basic-case simulation, the top product CH4 purity was 95.8 % with 90.9% recovery and the estimated mechanical energy consumption was 0.68 GJ/tonne-CH4. To find the optimal operating conditions, this study combined the simulation of 2-bed 8-step PSA process with design of experiments (DOE) method. After simulation analysis, the study showed a top product CH4 purity of 99.5% with 91.3% recovery, and 0.015 ppm H2S purity, which is suitable to be injected into the natural gas grid (>95% CH4), satisfying the standard of natural gas pipeline and can be used as fuel. The mechanical energy consumption was estimated to be 0.86 GJ/tonne-CH4.
Part Ⅱ:
In view of serious global warming problem and the massive energy waste in renewable energy, power-to-gas (P2G) is currently an energy storage technology actively promoted by the European Union. This technology includes water electrolysis and methanation reaction, and the latter often reacts with excess carbon dioxide. After the reaction, the gas composition is CO2, CH4, C2H6 and a small amount of H2. In this research, we will develop a CO2 purification technology from the outlet gas of methanation by simulation of pressure swing adsorption (PSA) process. First, we will find at least two commercial adsorbents from literature data and the data of adsorption isotherm by experiments. Then, we will establish a simulation program of dual-bed eight-step PSA to develop a CO2 PSA purification process with CO2 product purity above 70%.
In the first part of study, we found suitable commercial adsorbents based on literature data and experimental measurement of equilibrium adsorption. After calculating the selectivity of CO2/CH4 and CO2/C2H6, we chose the zeolite 13X produced by COSMO as the adsorbent in this study. In the second stage, we conducted the PSA simulation program CO2 purification with a dual-bed eight-step process. This research used 67.9% methane, 30% carbon dioxide and 2.1% ethane as the feed, and after the simulation, the study showed a top product CH4 purity of 84.66% with 95.53% recovery, a bottom product CO2 purity of 84.03% and waste CO2 purity of 91.30%, both reaching the target of 70% CO2 purity. Therefore, the process can recycle this product to the reaction of methanation, in order to reduce CO2 emissions and improve the efficiency of carbon cycle. |
