| 摘要: | 生質沼氣是有機廢棄物(包括都市污泥、農業廢棄物、動物排泄物及工業廢水等)經厭氧醱酵處理所產生之氣體產物，其平均成分為甲烷(60% ~ 70%)、二氧化碳(30% ~ 40%)、硫化氫(0 ~ 4000 ppm)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溫室氣體，又以甲烷其全球暖化潛勢(Global warming potential, GWP)為二氧化碳之25倍，對於溫室效應的影響力不容小覷，而硫化氫氣體會與水氣產生硫酸，易造成機器損壞及管線腐蝕，因此如能分離硫化氫，並回收生質沼氣中甲烷至高純度以供後續再生能源使用，亦能同時回收二氧化碳達到溫室氣體減量之效用，可謂一舉數得。本計畫擬以初步實驗伴隨數值模擬以變壓吸附程序(pressure swing adsorption, PSA)進行生質沼氣純化技術開發，依據文獻資料找尋適當之吸附劑，利用等溫吸附曲線實驗建立吸附平衡曲線模式，此外利用突破曲線實驗結果找尋合適模擬參數，並利用模擬突破曲線實驗數據驗證以確認吸附劑各參數之準確性。因實驗室安全考量，將生質沼氣中CH4以N2取代先進行N2/ CO2雙塔PSA實驗，並建立N2/ CO2 PSA模擬程式，將模擬計算結果與實驗數據相驗證，以確認PSA模擬程式之可靠度及準確性。接著以模擬程式比較N2/ CO2與CH4/ CO2分離結果之差異，以此差異性為基礎，第二年進而設計出分離生質沼氣中H2S/ CH4/ CO2三成分多塔變壓吸附程序模擬之研究，就不同操作變因進行探討，如吸附塔塔長，進料流率，進料壓力、真空壓力以及各步驟時間等，找出最適化操作條件，達到同時分離出高純度的甲烷(> 99%)與二氧化碳(> 95%)(達美國能源部要求之CO2封存標準)，以作為未來開發實廠商業化生質沼氣純化變壓吸附程序之設計基礎。 ;Biogas is a product during anaerobic digestion of organic waste, such as urban sludge, agricultural waste, livestock excreta and industrial effluents. Biogas typically contains 60-70% CH4 (methane), 30-40% CO2, 0-4000 ppm H2S and small amounts of other components. Methane purified from biogas can be used as high value fuel or used to produce chemical products. Methane and carbon dioxide are also the main greenhouse gases which result in global warming effect. Since the global warming potential (GWP) of methane is twenty-five times greater than that of carbon dioxide, the influence of methane on the global warming effect cannot be ignored. In the presence of water, hydrogen sulfide leads to corrosion damage on the instruments and pipelines. Therefore, the separation of CO2 and H2S from biogas for obtaining pure bio-methane and simultaneously highly concentrated CO2 for subsequent sequestration or utilization is important. Pressure swing adsorption (PSA) is one of the most known and established industrial processes for gas separation because of the low energy requirements, low capital investment cost, and simplicity of operation. In this study, we will develop a biogas purification technology by basic experiments and simulation of PSA process. First, we will find the suitable adsorbent from literatures and obtain the parameters of adsorption isotherm from adsorption measurements. To validate the accuracy of adsorbent parameters, we will verify the simulation with the experiment of breakthrough curves. For laboratory safety, we substitute N2 for CH4 in the biogas to employ the experiment and simulation of dual-bed PSA process for N2/ CO2 separation. The simulation program will be verified by comparison with the experimental data and confirm the accuracy of the PSA simulation. Finally, we compare the difference between the result of N2/ CO2 and CH4/ CO2 PSA system by simulation and, at the second year, design a PSA process for H2S/ CH4/ CO2 separation by simulation. After exploring the effects of variables such as bed length, feed pressure, vacuum pressure, and the time of each step, we will find the best operating conditions for obtaining high purity methane (> 99%) and carbon dioxide (> 95%) simultaneously. The results would be helpful to design commercial PSA process in the future. |
