水合作用改質氧化鈣捕獲溫室二氧化碳氣體之循環再生能力研究

Abstract

隨著溫室效應逐漸加劇，「京都議定書」也正式生效，二氧化碳捕獲與封存(Capture and Storage, CCS)成為勢在必行的技術，在眾多的二氧化碳捕獲技術中，利用氧化鈣(CaO)作為二氧化碳捕獲之材料有著高吸附容量、高選擇性、高吸附速率以及量充足且價格便宜等優勢。然而氧化鈣在循環吸/脫附後，有劣化、燒結的現象，使吸附容量銳減，大幅降低氧化鈣的利用率，導致需頻繁汰換氧化鈣，且未來吸附劑汰換將為決定其成本之重要因子。近年來有許多針對CaO改質以降低劣化情形之研究，其循環測試的結果，證實適當之改質可抑制CaO劣化之問題，並提昇CaO之利用率。本研究將氧化鈣進行液相與汽相水合作用機制改質後，進行二氧化碳吸附反應，與未改質之氧化鈣比較，發現吸附容量有較佳的表現，其中液相水合改質之吸附量提升達2倍以上；另外，於氧化鈣脫附反應的過程中通入水蒸汽作為輔助的載流氣體，可大幅提升脫附之速率，並藉由尾端冷凝之方式濃縮提升二氧化碳出流濃度，更有利於後續之碳儲存與再利用；而在循環吸脫附測試的研究結果顯示，儘管氧化鈣於反覆吸脫附後仍有劣化之情形發生，然在300℃的條件下，通入水蒸汽與氧化鈣反應，能使氧化鈣之吸附容量再活化至新鮮狀態，並再應用於循環吸脫附中，最後利用SEM與BET特性分析探討氧化鈣孔洞分佈與吸附容量之關係，發現氧化鈣吸附容量劣化之主要原因為孔徑100 Å以上的孔洞體積，因燒結導致CaO顆粒彼此間隙減少所導致，顯示若能有效控制CaO顆粒間之距離，則可減緩或完全抑制劣化之情形。

Due to that fossil fuel combustion causes increasing atmospheric concentration of CO2 and induces manmade greenhouse effect, the decrease of anthropogenic CO2 emissions has gained worldwide attention. The CaO cyclic capture is one of the promising CO2 capture technologies which has the advantages of low sorbent purchase cost and high fresh sorbent capacity. However, CaO is also suffered from severe decay in sorbent capacity during cyclic adsorption. In this study, the modification on CaO as well as the adsorption-desorption-regeneration process to enhance the uptake capacity and reversibility were been researched. The CaO is modified by either metal addition or hydration process. The result showed that low-temperature steam and liquid water hydration process are promising to improve sorbent CO2 adsorption capacity, While, steam desorption at 850℃ could enhance the CO2 desorption rate, The reversibility test showed that after the deterioration of CaO sorbent, using the 300 □C steam could reactivate the CaO and the CO2 adsorption capacity was the same as the fresh sorbent again. From SEM and BET results, the main reason for the decay of CaO adsorption capacity is due to pore volume of larger pore size (>100Å) was decreasing.