二氧化碳地質封存為二氧化碳減量的有效方法之一，地質封存是指將二氧化碳注入到油氣田、深部鹽水層或煤層。本實驗目的在於探討在台灣地區將二氧化碳封存於煤層之可行性，20個來自台灣中北部中新世煤層之樣本，分別為木山層、石底層和南莊層，採用壓力體積測量法將二氧化碳注入煤樣，模擬地下煤層壓力條件，實驗數據由Langmuir Isotherm model 進行 Langmuir Pressure 及Langmuir Volume 參數擬合。實驗首先將樣本粉碎至60 mesh，在烘箱加熱至100℃脫水後，放置到儲煤罐中抽真空並逐步增加壓力至800 psi，接著逐步減壓以觀測壓力變化對吸脫附的影響，並檢視吸脫附作用所造成的遲滯現象。再將煤樣工業分析及煤岩分析之結果和吸附量對比後，發現固定碳，煤級及鏡煤素含量與吸附量成正相關，而固定碳及鏡煤素含量與孔隙大小亦有相關性，所以推測孔隙大小會影響吸附量。本實驗吸脫附結果顯示，台灣煤樣氣體吸附量約250 scf/ton ~500 scf/ton。根據Langmuir Isotherm model 分析結果，以大東山煤礦煤樣對二氧化碳等溫吸脫附量為最高，可能原因為在烘乾前內含水份填充於孔隙中，而烘乾後產生較多孔隙造成吸附量增加。掃描式電子顯微鏡影像顯示以黏土礦物為主之礦物質填充孔隙，為導致氣體吸附量下降之主因。 Geological sequestration of CO2 into depleted oil reservoir, saline aquifer or unmineable coal seam is now being actively investigated for the purpose of reducing greenhouse gas in the atmosphere. Understanding the physical, chemical, and thermodynamic phenomena occurred with CO2 injection is very important in making a reliable prediction of sequestration. This study examined the feasibility of carbon dioxide sequestration into unmineable coal seams in Taiwan. A total of 20 Miocene-aged coal samples from Western Foothill Belt, NW Taiwan, were collected. The stratigraphy include Mushan, Shihti, and Nanchuang Formation from bottom up. Proximate and petrographic analyses include maceral composition and vitrinite reflectance were also measured. Carbon dioxide adsorption isotherms were analyzed at 35℃ and up to 800 psi, by using a gravimetric ad/desorption apparatus. Isotherms were then fitted with a modified Langmuir Isotherm model by using Langmuir Pressure and Langmuir Volume so the model can be applied to supercritical conditions. According to the result of adsorption experiment, the pressure and temperature were quite significant. The gas storage capacity of CO2 was about 250~500 scf/ton at pressure up to 800 psi. Comparing the results of adsorption capacity with Proximate and Petrographic analyses, the Langmuir Volume shows a strong positive correlation with fixed carbon and vitrinite content. Furthermore, Adsorption capacity is closely related to micropores which were also rank and maceral dependent. It is noticed that the observed coal pore structures were affected by rank, and thus exhibit different diffusion rate. Finally, images under SEM were evaluated to understand the pathways of gas sorption.The filling mineral matter (mostly clay) will lead to the decrease of gas sorption.
