沼氣中二氧化碳與甲烷氣體之吸附分離技術開發(I)

Abstract

甲烷(CH4)與二氧化碳(CO2)均為溫室效應氣體，而沼氣中同時含有此兩 種溫室氣體，以往沼氣因為缺乏經濟效益而任意排放至大氣中，造成溫室 氣體濃度增加。而隨著國際間對溫室效應與新能源開發之日益重視，如果 能發展出從沼氣中將CH4 與CO2 分離之技術，可以將沼氣濃縮純化，成為 具高能源價值之甲烷燃料，並同時減少二氧化碳溫室氣體之排放，可謂一 舉兩得。 本計畫即提出以商用沸石利用物理吸附法從沼氣中吸附 CO2，以便與 CH4 氣體分離之研究，期能發展出最具經濟效益之沼氣純化技術。本計畫將 分兩年進行，本年度計畫為第一年計畫。在第一年計畫中，將找出可分離 CO2 與CH4 之最佳沸石原材與金屬改質後之沸石，分析其對CO2/CH4 之選 擇度，並了解沼氣純化受溫度與濕度之影響。第二年則將探討胺基改質沸 石之可能性，並將進行溫變式(temperature swing adsorber, TSA)與壓變式 (pressure swing adsorber, PSA)反覆吸脫附反應器之設計、成本效益與耗能分 析。本計畫第一年度預期對CO2 之工作吸附容量(working capacity)能達到 40mg/g 以上，而在第二年度則將可再提升至60mg/g 以上。本計畫在分析比 較TSA 與PSA 之反覆吸脫附效能、成本效益與耗能後，將可提供實廠應 用於沼氣純化之參考依據。

Both methane (CH4) and carbon dioxide (CO2) are greenhouse gases which present in the biogas. The emission sources of biogas include wastewater plants, agriculture wastes and landfills, etc. If not properly treated, the biogas is one of the major sources of greenhouse gas emissions. However if the CO2 in the biogas can be separated from the CH4, then the heating value of biogas can be greatly enhanced and the greenhouse gas emissions can be reduced at the same time. This study intends to use the commercial zeolites and modify them so that they will contain active metals for the separation of CH4/CO2. This is a two year-project, in the first year we will test several possible types of zeolites and evaluate the activities of different metal species on the selectivity of CH4/CO2. In addition, the effects of moisture and temperature of the biogas on the CH4/CO2 separation will also be investigated. In the second year, we will investigate the possibility of using amine reagents for the modification of commercial zeolites. Furthermore, the key design parameters for the temperature swing adsorber (TSA) and pressure swing adsorber (PSA) will be evaluated. And the cost effectiveness and the energy consumption of these two types of reactors will be compared. It is expected that at the end of the first year project the working capacity of the zeolite adsorbent will be at least 40 mg/g, while at the end of the second year project it will be larger than 60 mg/g. The results of this study will provide valuable information for the purification of biogas.