本研究係以澳洲鐵礦製成載氧體，並添加鹼金屬與鹼土金屬修飾載氧體，評估其對化學迴圈燃燒程序之促進效果，使用成本低廉的煙煤及無煙煤為燃料，於半套式流體化床進行煤炭直接進料化學迴圈燃燒反應。
首先以石英砂與兩種燃料進行氣化反應，藉由調整反應溫度及水蒸氣含量，找出最佳氣化反應條件，結果顯示在反應溫度950℃，水蒸氣含量52 vol%，煙煤及無煙煤氣化時間分別為20和40分鐘，此反應條件下碳捕獲效率可達100%。煙煤與載氧體反應時，其金屬助觸媒促進效果並不顯著，CO2純度皆約為63-78%，因為煙煤含有高達33.8 wt%的揮發性物質，使載氧體無法有足夠時間與還原氣體反應，而使用無煙煤當燃料，揮發性物質僅為8.83 wt%，氣化速率緩慢，載氧體有較長接觸反應時間，可將還原氣體轉化成CO2，鐵礦載氧體CO2純度為76%，而添加鈉、鈣助觸媒之載氧體可將CO2純度提升至92-94%，但鈉改質載氧體，反應後有明顯聚集現象，造成去流化現象。鉀改質載氧體，可明顯提升無煙煤氣化速率，但因反應時間不足而導致CO2純度過低，進一步降低鉀金屬含量以及反應溫度時，減緩氣化速率，CO2純度可提升至94%，且於氧化階段無未燃燒焦碳及積碳現象，顯示煤炭氣化速率對CO2純度有顯著影響。
在多次迴圈反應實驗結果顯示，添加鉀改質載氧體，對煤炭催化活性有顯著失活現象，因為鉀金屬透過離子自身擴散進入到載氧體內部所導致，而添加鈣改質載氧體，則顯示有良好的高CO2純度、高碳捕獲效率及反應穩定性，且無明顯聚集現象，因此，使用AB-Ca為本研究中最佳載氧體，將可作為具有實用性之載氧體。

In this study, the oxygen carriers were prepared by an impregnation method using natural hematite from Australia as the raw material and alkali and alkaline-earth salts as the additives. The coal direct chemical looping combustion (CDCLC) process in a fluidized bed was used to evaluate the reactivity of different oxygen carriers using bituminous coal and anthracite as fuel, respectively.
At the beginning of this work, effects of reaction temperature and steam content on coal gasification using quartz sand were investigated. The results indicated the complete gasification time for bituminous coal and anthracite are 20 and 40 minutes at 950 oC under an atmosphere of 52 vol% steam. The metal-modification procedure on oxygen carrier reacts does not show the significant improvement in the CDCLC with using bituminous coal. The bituminous coal has a rapid gasification rate to produce plenty of volatile gases, resulting in the insufficient reaction time with oxygen carriers. Therefore, the low CO2 purity was obtained in this CDCLC experiment. In contrast to bituminous coal, the anthracite possesses a lower gasification rate due to its highly fixed carbon content. Oxygen carriers thus exhibit longer contact time to convert fuel gases to CO2 and H2O. The CO2 purity in this CDCLC was enhanced from 76% to 92-94% in the presence of sodium and calcium additive. The defluidization phenomena of this system with using sodium-modified oxygen carriers were observed due to a serious aggregation effect. Moreover, the gasification rate of anthracite can be increased with the increase in the potassium content of oxygen carrier, meanwhile, the CO2 purity is decreased by decreasing reaction time with oxygen carrier. The CO2 purity of 94% was reached with the decrease in reaction temperature and loading amount of potassium salt. It indicates the coal gasification rate play an important role in the CO2 purity of CDCLC process.
The results of multi-cycle of CDCLC show the activity of potassium-modified oxygen carrier is decreased gradually as the cycle time increases. It is probably due to potassium ions diffuse into the interior of oxygen carrier. The calcium-modified oxygen carrier exhibits excellent stable activity, high CO2 purity and good efficiency for carbon capture during the long-term CLC test in the fluidized-bed system.
In conclusion, AB-Ca was the best oxygen carrier in this study, which can be a practical oxygen carrier in chemical looping combustion process.

[1] International Energy Agency, “IEA Energy Technology Prospective 2010”, OECD/IEA, 48 (2010).
[2] 胡均立、林瑞珠, “台灣推動碳捕捉與封存技術之經濟可行性初探”, 經濟前瞻，中華經濟研究院, pp. 63-72 (2010).
[3] 我國碳捕集技術介紹與展望,徐恆文,工業技術研究院綠能與環境研究所, CCS減量技術研討會(2011).
[4] 朱敬平, “化學迴圈燃燒技術發展現況簡介”, 中興工程季刊, 第110期, pp. 63-72 (2011).
[5] Fan, L. S., “Chemical looping systens for fossil energy conversions”, Hoboken, New Jersey Published simultaneously in Canada:John Wiley & Sons (2010).
[6] Zhang, J.; Guo, Q.; Liu, Y.; Cheng, Y., “Preparation and characterization of Fe2O3/Al2O3 using the solution combustion approach for chemical looping combustion”, Industrial & Engineering Chemical Research, 51, pp. 12773-12781 (2012).
[7] Wen, Y. Y.; Li, Z. S.; Xu, L.; Cai, N. S., “Experimental study of natural Cu ore particles as oxygen carriers in chemical looping with oxygen uncoupling”, Energy and Fuels, 26, pp. 3919-3927 (2012).
[8] Bidwe, A. R.; Mayer, F.; Hawthorne, C.; Charitos, A.; Schuster, A.; Scheffknecht, G., “Use of ilmenite as an oxygen carrier in chemical looping combustion-batch and continuous dual fluidized bed investigation”, Energy Procedia, 4, pp. 433-440 (2011).
[9] Cuadrat, A.; Abad, A.; Adanez, J.; de Diego, L. F.; Labiano, F. G.; Gayan, P., “Behavior of ilmenite as oxygen carrier in chemical-looping combustion”, Fuel Processing Technology, 94, pp. 101-112 (2012).
[10] Azis, M. M.; Jerndal, E.; Leion, H.; Mattisson, T.; Lyngfelt, A., “On the evaluation of synthetic and natural ilmenite using syngas as fuel in chemical-looping combustion (CLC)”, Chemical Engineering Research and Design, 88, pp. 1505-1514 (2010).
[11] Stainton, H.; Ginet, A.; Surla, K.; Hoteit, A., “Experimental investigation of CLC coal combustion with nickel based particles in a fluidized bed”, Fuel, 101, pp. 205-214 (2012).
[12] Gu, H.; Shen, L.; Xiao, J.; Zhang, S.; Song, T., “Chemical looping combustion of biomass/coal with natural iron ore as oxygen carrier in a continuous reactor”, Energy and Fuels, 25, pp. 446-455 (2011).
[13] Shen, L.; Wu, J.; Xiao, J.; Song, Q.; Xiao, R., “Chemical looping combustion of biomass in a 10 kWth reactor with iron oxide as an oxygen carrier”, Energy and Fuels, 23, pp. 2498-2505 (2009).
[14] Cuadrat, A.; Abad, A.; de Diego, L. F.; Labiano, F. G.; Gayan, P.; Adanez, J., “Prompt considerations on the design of chemicall ooping combustion of coal from experimental tests”, Fuel, 97, pp. 219-232 (2012).
[15] Abad, A.; Adanez, J.; Cuadrat, A.; Labiano, F. G.; Gayan, P.; de Diego, L. F., “Kinetics of redox reactions of ilmenite for chemical-looping combustion”, Chemical Engineering Science, 66, pp. 689-702 (2011).
[16] Browm, T. A.; Dennis, J. S.; Scott, S. A.; Davidson, J. F.; Hayhurst, A. N., “Gasification and chemical-looping combustion of a lignite char in a fluidized bed of iron oxide”, Energy and Fuels, 24, pp. 3034-3048 (2010).
[17] Saha, C.; Bhattacharya, S., “Comparison of CuO and NiO as oxygen carrier in chemical looping combustion of a Victorian brown coal”, International Journal of Hydrogen Energy, 36, pp. 12048-12057 (2011).
[18] Yang, J. B.; Cai, N. S.; Li, Z. S., “Reduction of iron oxide as an oxygen carrier by coal pyrolysis and steam char gasification intermediate products”, Energy and Fuels, 21, pp. 3360-3368 (2007).
[19] Keller, M.; Leion, H.; Mattisson, T.; Lyngfelt, A., “Gasification inhibition in chemical-looping combustion with solid fuels”, Combustion and Flame, 158, pp. 393-400 (2011).
[20] Luo, M.; Wang, S.; Wang, L.; Lv, M.; Qian, L.; Fu. H., “Experimental investigation of co-combustion of coal and biomass using chemical looping technology”, Fuel Processing Technology, 110, pp. 258-267 (2013).
[21] Miles, T. R., “Alkali deposits found in biomass power plants: a preliminary investigation of their extent and nature”, National Renewable Energy Laboratory (1995).
[22] Bao, J.; Li, Z.; Cai, N., “Experiments of char particle segregation effect on the gas conversion behavior in the fuel reactor for chemical looping combustion”, Applied Energy, 113, pp. 1874-1882 (2014).
[23] Xiao, R.; Song, Q.; Song, M.; Lu, Z.; Zhang, S.; Shen, L., “Pressurized chemical-looping combustion of coal with an iron ore-based oxygen carrier”, Combustion and Flame, 157, pp. 1140-1153 (2010).
[24] Liu, L.; Zachariah, M. R., “Enhanced performance of alkali metal doped Fe2O3 and Fe2O3/Al2O3 composites as oxygen carrier material in chemical looping combustion”, Energy and Fuels, 27, pp. 4977-4983 (2013).
[25] Yu, Z.; Li, C.; Fang, Y.; Huang, J.; Wang, Z., “Reduction rate enhancements for coal direct chemical looping combustion with an iron oxide oxygen carrier”, Energy and Fuels, 26, pp. 2505-2511 (2012).
[26] Yu, Z.; Li, C.; Jing, X.; Zhang, Q.; Fang, Y.; Zhao, J.; Huang, J., “Effects of CO2 atmosphere and K2CO3 addition on the reduction reactivity, oxygen oransport capacity, and sintering of CuO and Fe2O3 oxygen oarriers in coal direct chemical looping combustion”, Energy and Fuels, 27, pp. 2703-2711 (2013).
[27] Arjmand, M.; Leion, H.; Mattisson, T.; Lyngfelt, A., “Investigation of different manganese ores as oxygen carriers in chemical looping combustion for solid fuels”, Applied Energy, 113, pp. 1883-1894 (2014).
[28] Spiro, C. L.; McKee, D. W.; Kosky, P. G.; Lamby, E. J., “Observation of alkali catalyst particles during gasification of carbonaceous materials in CO, and steam”, Fuel, 63, pp. 686-691 (1984).
[29] Kwon, T. W.; Kim, J. R.; Kim, S. D.; Park, W. H., “Catalytic steam gasification of lignite char”, Fuel, 68, pp. 416-421 (1989).
[30] Keller, M.; Leion, H.; Mattisson, T., “Mechanisms of solid fuel conversion by chemical-looping combustion (CLC) using manganese ore: catalytic gasification by potassium compounds”, Energy Technology, 1, pp. 273-282 (2013).
[31] Arjmand, M.; Leion, H.; Lyngfelt, A.; Mattisson, T., “Use of manganese ore in chemical-looping combustion—Effect on steam gasification”, International Journal of Greenhouse Gas Control, 8, pp. 56-60 (2012).
[32] Ryden, M.; Arjmand, M., “Continuous hydrogen production via the steameiron reaction by chemical looping in a circulating fluidized-bed reactor”, International Journal of Hydrogen Energy, 37, pp. 4843-4854 (2012).
[33] Chen, S.; Shi. Q.; Xue, Z.; Sun, X.; Xiang, W., “Experimental investigation of chemical-looping hydrogen generation using Al2O3 or TiO2-supported iron oxides in a batch fluidized bed”, International Journal of Hydrogen Energy, 36, pp. 8915-8926 (2011).
[34] 祝以湘、陳榮欽、封雷, “K2O Fe2O3系催化劑的穆斯堡爾譜研究”, 中國物理化學學報, 第15卷, 第3期, pp. 234-240 (1999).
[35] Maensiri, S.; Sangmanee,; Wiengmoon, A., “Magnesium ferrite (MgFe2O4) nanostructures fabricated by electrospinning”, Nanoscale Research Letter, 4, pp. 221-228 (2009).
[36] Johansson, M.; Mattisson, T.; Lyngfelt, A., “Investigation of Fe2O3 with MgAl2O4 for chemical-looping combustion”, Industrial & Engineering Chemical Research, 43, pp. 6978-6987 (2004).
[37] Wen, C. Y.; Yu, Y. H., “A generalized method for predicting the minimum fluidization velocity”, American Institute of Chemical Engineers Journal, 12, pp. 610-612 (1996).