隨著人類生活的進步，亦加劇環境變遷，故人們對環保的意識日漸抬頭，溫室氣體的排放亦成為各國關注之議題，為達到節能減碳的目的，煉鐵工藝也跟著推陳出新。
其中，碳熱還原煉鐵製程僅須將鐵碳複合球團置於高溫下(1250℃以上)，即會發生快速熱還原反應，在短時間(約20分鐘)內，即可得到高金屬化率之直接還原鐵 (Direct Reduced Iron, DRI)。此製程相較於傳統高爐煉鐵製程，可免除鐵礦燒結和煤炭煉焦兩前處理製程，故具節能減碳之潛力。相較於 RHF製程之1~1.5顆球團佈料，高料層佈料被證實有突破 RHF製程之 DRI金屬化程度和產率偏低之瓶頸。高料層佈料功效必須建立在料層內部有高度輻射熱傳之穿透，因此在高溫還原過程中，球團能維持顆粒完整且高度收縮便成生球之基本特性要求。

為探討球團於還原過程中產生收縮變化之原因，本研究進行一系列碳熱還原試驗，於試驗過程中，以光學影像技術連續紀錄球團外觀變化並計算其投影體積收縮率，目的在探討複合球團收縮之影響因素。此外，選擇不同時間點進行球團試樣淬冷，觀察球團內部顯微結構及分析元素分布與鐵金屬化率，以推論造成球團膨脹及收縮的可能機制。並藉由改變還原劑種類及揮發分含量來討論對球團收縮變化之影響。

實驗結果顯示，球團開始收縮時，同時為Boudouard reaction發生且伴隨著大量還原反應，由顯微結構可觀察到金屬鐵顆粒燒結，而在球團收縮趨緩時才有渣相連續相生成，故渣相液相燒結對球團收縮影響有限，主要由鐵粒燒結造成球團收縮之現象。而不同揮發分 (Volatile Matter, VM)含量的煤鐵礦複合球團之體積變化差異不大，因揮發分作用區域於1000 oC以上已較不顯著，故揮發分含量對球團收縮變化影響有限。而還原劑種類則會影響球團有最大收縮速率的溫度，高VM煤與 coalchar的複合球團約在1000 oC，無煙煤複合球團約在1050 oC，高VM煤與石墨的複合球團則約在1100 oC，還原劑的反應性則為高 VM煤最大，無煙煤次之，石墨最小，故反應性較大的還原劑會使球團在較低的溫度進行大量還原反應，由球團外觀上觀察到發生收縮變化的時間較早，且還原後之球團可維持球團形狀的機率亦較高。

In recent years, environmental issues have been taken seriously in order to save energy and to reduce carbon emissions. The ironmaking process has followed this innovation. The tall-bed ironmaking processes, inside the material layer, must have a high degree of radiant heat penetration. Also, it is necessary to maintain the integrity of the pellets and have a high degree of volume shrinkage after reduction. This study discusses the impact of different reductants on the shrinkage behavior of composite pellets during carbothermic reduction. Throughout the experiment, an in-situ digital camera records the morphological and volume changes during the reductions. Interrupted experiment is used to observe the microstructure and elemental composition of pellets by SEM, and the phase composition changes of pellets by XRD analysis and chemical analysis. DSC analysis is used to observe the reactions that occurred during the reduction process and to infer the effect of the shrinkage behavior of the pellets. Experimental results show that iron oxide-carbon composite pellets have the largest volume swelling degree (about 5 %) at 600 oC. After the Boudouard reaction and reduction occurs, the formation and sintering of iron particles lets the pellets shrink dramatically (approximately 70 %). The reductant reactivity of composite pellets is better, which makes the pellets generate metallic iron at lower temperatures, and the pellets also start to shrink at lower temperature. By the end of the experiment, the probability of maintaining a ball-shape is higher.

1.Harada, T, and Tanaka, H., “Future Steelmaking Model by Direct Reduction Technologies”, ISIJ International, 51(8), pp.1301-1307, (2011).
2.陳玉松編撰，“永續發展的綠色材料─鋼鐵”，科學發展月刊，第486期，pp.6-9, 2013年.
3.Bellevrat, E, and Menanteau, P., “Introducing carbon constraint in the steel sector: ULCOS scenarios and economic modeling”, Proceedings of the 4th Ulcos seminar. (2008).
4.Quader, M. A., Ahmed, S., Ghazilla, R. A. R., Ahmed, S., and Dahari, M., “A Comprehensive Review on Energy Efficient CO2 Breakthrough Technologies for Sustainable Green Iron and Steel Manufacturing”, Renewable and Sustainable Energy Reviews, 50, pp.594-614, (2015).
5.Quader, M. A., Ahmed, S., Dawal, S. Z., & Nukman, Y., “Present Needs, Recent Progress and Future Trends of Energy-Efficient Ultra-Low Carbon Dioxide (CO2) Steelmaking (ULCOS) Program”, Renewable & Sustainable Energy Reviews, 55, pp.537-549, (2016).
6.陳秉詮編撰，“煉鋼製程的節能減碳”，科學發展月刊，第486期，pp.20-24，2013年.
7.Harada, T., Tsuge, D., Kobayashi, I., Tanaka, H., and Uemura, H.,. “The Development of New Iron Making Processes”, Kobelco technology review, 26, pp.92-97, (2005).
8.Lu, W. K., and Huang, D. F., “The Evolution of Ironmaking Process Based on Coal-Containing Iron Ore Agglomerates”, ISIJ International, 41(8), pp.807-812, (2001).
9.張皓荀編撰，“煤鐵礦複合球團於不同溫度歷程之碳熱還原和形貌變化研究”，國立成功大學碩士論文，2015年7月
10.Kikuchi, S., Ito, S., Kobayashi, I., Tsuge, O., and Tokuda, K., “ITmk3@Process”, Kobelco technology review, 29, pp.78-84, (2010).
11.蔡辛慈編撰，“新煉鐵製程法之介紹”，化工技術，第12卷第12期，pp.147-164，2004年.
12.Oda, H., Ibaraki, T., and Abe, Y., “Dust Recycling System by the Rotary Hearth Furnace”, Nippon Steel Technical Report, 94, pp.147-152, (2006).
13.劉世賢編撰，“鋼鐵廠固雜料產出及其資源化技術介紹”，中工高雄會刊，第18卷第2期,pp.56-63，2010年.
14.Hasanbeigi, A., Arens, M., and Price, L., “Alternative Emerging Ironmaking Technologies for Energy-Efficiency and Carbon Dioxide Emissions Reduction: A Technical Review”, Renewable and Sustainable Energy Reviews, 33,pp. 645-658, (2014).
15.Chowdhury, G. M., Murmu, C. S., Roy, S. K., and Roy, G. G., “Some Studies to Establish the Reaction Mechanism for the Reduction of Iron Ore-Graphite Composite Pellets in a Packed Bed Reactor”, Steel Research International, 81(11), pp.925-931, (2010).
16.Moon, J., and Sahajwalla, V., “Investigation into The Role of the Boudouard Reaction in Self-Reducing Iron Oxide and Carbon Briquettes”, Metallurgical and Materials Transactions B, 37(2), pp.215-221, (2006).
17.Wei, R. F., Cang, D. Q., Zhang, L. L., and Bai, Y. y., “Staged Reaction Kinetics and Characteristics of Iron Oxide Direct Reduction by Carbon”, International Journal of Minerals, Metallurgy, and Materials, 22(10), pp.1025-1032, (2015).
18.Nasr, M. I., Omar, A. A., Hessien, M. M., and Ei-Geassy, A. A., “Carbon Monoxide Reduction and Accompanying Swelling of Iron Oxide Compacts”, ISIJ international, 36(2), pp.164-171, (1996).
19.Hayashi, S., and Yoshiaki, I., “Abnormal Swelling during Reduction of Binder Bonded Iron Ore Pellets with CO-CO2 Gas Mixtures”, ISIJ International, 43(9), pp.1370–1375, (2003).
20.Dwarapudi, S., Banerjee, P. K., Chaudhary, P., Sinha, S., Chakraborty, U., Sekhar, C., Venugopalan, T., and Venugopal, R., “Effect of Fluxing Agents on the Swelling Behavior of Hematite Pellets”, International Journal of Mineral Processing, 126, pp.76-89, (2014).
21.Seaton, C. E., Foster, J. S., and Velasco, J., “Structural Changes Occurring during Reduction of Hematite and Magnetite Pellets Containing Coal Char”, ISIJ International, 23(6), pp.497-503, (1983).
22.Wang, H., and Sohn., H.T., “Effects of Firing and Reduction Conditions on Swelling and Iron Whisker Formation during the Reduction of Iron Oxide Compact”, ISIJ International, 51(6), pp.906–912, (2011).
23.Sharma, T., Gupta, R. C., and Prakash, B., “Effect of Firing Condition and Ingredients on the Swelling Behavior of Iron Ore Pellets”, ISIJ International,. 33(4), pp.446-453, (1993).
24.Tejasukmana, A., Fruehan, R. J., and Pistorius, P. C., “Controlling Shrinkage during the Reduction of Composite Iron Ore-Reductant Pellets”, CISR Progress Report, (2011).
25.Tejasukmana, A., Fruehan, R. J., and Pistorius, P. C., “Controlling Shrinkage during the Reduction of Composite Iron Ore-Reductant Pellets”, CISR Progress Report, (2012).
26.Tejasukmana, A., Li, W. and Pistorius, P. C., “The Effect of Reductant Type on the Shrinkage Behavior of Composite Iron Ore-Carbon Reductant Pellets during Reduction”, CISR Progress Report, (2012).
27.Fruehan, R. J., “Sustainable Steelmaking Using Biomass and Waste Oxides (TRP9902)”. American Iron and Steel Institute (US), (2004).
28.Zuo, H.-b., Hu, Z.-w., Zhang, J.-l., Li, J., and Liu, Z.-j., “Direct Reduction of Iron Ore by Biomass Char”, International Journal of Minerals, Metallurgy, and Materials, 20(6), pp.514-521, (2013).
29.Fu, J.-X., Zhang, C., Hwang, W.-S., Liau, Y.-T., and Lin, Y.-T., “Exploration of Biomass Char for CO2 Reduction in RHF Process for Steel Production”, International Journal of Greenhouse Gas Control, 8, pp.143-149, (2012).
30.Merrick, D., “Mathematical Models of the Thermal Decomposition of Coal: 1. The Evolution of Volatile Matter”, Fuel, 62(5), pp.534-539, (1983).
31.Takyu, Y., Murakami, T., Son, S. H., and Kasai, E., “Reduction Mechanism of Composite Consisted of Coal and Hematite Ore by Volatile Matter at 700–1100 K”, ISIJ International, 55(6), pp.1188-1196, (2015).
32.Wang, G., Ding, Y.-g., Wang, J.-s., She, X.-f., and Xue, Q.-g., “Effect of Carbon Species on the Reduction and Melting Behavior of Boron-Bearing Iron Concentrate/Carbon Composite Pellets”, International Journal of Minerals, Metallurgy, and Materials, 20(6), pp.522-528, (2013).
33.Biswas, A. K., “Principles of Blast Furnace Ironmaking”, Cootha Publishing House, (1981)