煉鐵工業使用高爐至今已超過五百年，而在這段期間逐漸演變成高效率且高能效的反應器，目前高爐仍是全世界主要的產鐵設備，然而，高爐不僅需要焦炭作為還原劑，其煉焦廠的價格昂貴且衍生許多相關的環境問題，例如：二氧化碳的排放與顆粒物質的汙染；此外，塊狀材料與高品料的價格亦有上漲的趨勢，故許多鋼鐵工業致力於開發新型的煉鐵製程，以期降低汙染處理的成本並提高反應效率。
　　高料層煉鐵製程屬於煤基直接還原法，還原劑部分則可直接使用未經過煉焦製程的碳來源，目前的研究大部分將鐵礦與煤礦混合造粒成煤鐵礦複合球團後，堆疊7~8層的料堆並使用熱空氣由上方進行球團加熱，使其在高溫下進行碳熱還原反應，最終產出高金屬化率的直接還原鐵。其中煤基直接還原法與傳統高爐煉鐵最大的差異，在於前者使用的還原劑可為非冶金煤，生質煤的使用也具有可行性。
　　而除了煤礦、生質炭中的固定碳作為主要的還原劑，升溫過程中煤礦亦會釋出揮發分並裂解成具有還原性的CO、H2、CH4等小分子氣體幫助鐵礦還原，又隨著升溫歷程及還原劑的不同，VM裂解的狀況也會有所改變，故還原劑在升溫歷程中的裂解產氣亦是一個觀察依據，可協助解釋鐵礦的還原過程。
　　又在高料層碳熱還原煉鐵製程中，若球團產生軟熔崩塌、膨脹的狀況，會使整個料層的熱傳受到阻礙，進而使整體料堆的反應狀況受到影響，降低了金屬化率及金屬鐵產率；若球團具有良好的收縮率且沒有軟熔崩塌現象，輻射熱傳將不受阻礙地從上層傳遞到下層，使整體料堆具有良好的還原狀況，也能夠達到高金屬化率及金屬鐵產率。
　　焙燒處理為一種生質物前處理方式，能有效提升固定碳含量、研磨性與密度，並降低水分與揮發分以提升能源密度，同時可以使焙燒後產物具有疏水性以利後續運輸與保存；而對於本研究，固定碳含量為鐵礦碳熱還原反應中最主要的還原劑，並可有效提高直接還原鐵的產率。
　　為探討農業廢棄物如：稻草、廢棄菇包等對於鐵礦在碳熱還原過程中的熔融性質與還原反應影響，本研究使用不同種類的農業廢棄物與鐵礦製成的複合球團，利用還原過程影像紀錄、化學分析等討論球團軟熔崩塌的成因，並利用氣體分析儀量測不同升溫歷程下複合球團的產氣狀況與揮發份的裂解狀況(即乾餾生質煤的產氣狀況)，以此基準下定量並比較不同種類生質物對球團還原的影響。

Blast furnace is still the main ironmaking equipment around the world, but the pollution from sintering and coking causes huge processing costs and environmental issues, eco-friendly ironmaking processes are under development. Among them, PSH ironmaking process is the potential methods to reduce greenhouse gas emission.
Torrefaction is a treatment for biomass which increasing fixed carbon content, energy density and grindability, and decreasing the volatile matter. For our experiments, fixed carbon content is the most important property because it’s the main reducing agent during carbothermic reduction.
In this study, we experiment with the reduction of the composite pellets under three different heating rates and different agricultural wastes as reducing agent. We use interrupted experiments and chemical analysis to find out the reduction process, and use CCD, gas analyzer to monitor the whole reaction which can provide us continuous and instant data about the pellets.
The results shows that using torrefied biomass as reducing agent for composite pellets during carbothermic reduction would get more DRI production than using untorrefied biomass, but it’s still lower than we use coal as reducing agent. Besides, some problems also appear like: reducing the strength of original composite pellets and stackability, slowing down the reduction rate and swelling phenomenon happening during the reaction.

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