α-氧化鐵填充床併同處理燃燒廢氣中氮氧化物/未燃碳之研究

Simultaneous Removal of Nitrogen Oxide and Unburned Carbon from Flue Gas by α-Fe2O3 Packed Bed

溫正安(Zheng-An Wen)

指導教授 ： 陳孝行

國立臺北科技大學/工程學院/環境工程與管理研究所/碩士(2008年)

摘要

本研究係以微米級(d ≦ 45 μm)α-氧化鐵粉(α-Fe2O3)與活性碳粉混合於填充床，利用活性碳粉來模擬燃燒廢氣中之未燃碳，藉由反應溫度、一氧化氮(NO)進流濃度、α-氧化鐵粉添加量、碳粉添加量及含氧(O2)濃度等反應因子，探討α-氧化鐵觸媒系統處理NO之可行性研究，並由反應後鐵粉之XRD (X光粉末繞射光譜儀)分析結果，推估可能的反應機制。
α-氧化鐵之Fe3+已為最高氧化態，本身無法還原NO氣體，因此需要還原性氣體CO先還原α-氧化鐵中的Fe3+為Fe2+，才具有處理NO之能力。在反應溫度623 K以下時，由於反應溫度較低，碳粉無法有效地與O2發生化學反應，因此無法產生足夠的還原性氣體CO，造成Fe3+還原成Fe2+之累積量不足，故無法完全去除NO；反應溫度673 ~ 773 K時，NO去除效率在反應初期皆可達到100%，表示累積之Fe2+較充足，隨著溫度的提升，反應穿透時間及NO去除量也隨之增加。NO進流濃度960 ppmv以下時，於反應時間16320秒以前，NO去除效率皆可達到100%，且NO去除量隨著NO進流濃度增加而提高，呈線性遞增關係。α-氧化鐵粉添加量低於0.5 g時，無法100%去除NO氣體，顯示提供之α-氧化鐵觸媒表面積不足，故α-氧化鐵粉與CO反應產生之Fe2+量較低；當α-氧化鐵粉添加量為0.5 g以上時，反應系統已提供足夠之固體活化表面，因此能達到100%之NO去除效率。碳粉添加量多寡會影響其和O2反應之時間長短，增加碳粉量可延長CO氣體出流之持續時間，相對地穿透時間與NO去除量也隨之增加，並呈線性正相關。煙氣含氧濃度效應方面，O2進流濃度由3%增為6%、9%及12%時，穿透時間及NO去除量隨著O2進流濃度增加而減少，為一遞減之曲線。由XRD分析結果，進一步瞭解α-氧化鐵在反應機制中為一觸媒，碳粉在整體反應中為提供還原性氣體CO之角色，而CO將觸媒表面之Fe3+還原為Fe2+後，Fe2+再還原NO為N2，總反應式如下：
C+1/2O2→1/2N2+CO2

關鍵字

α-氧化鐵 ； 未燃碳 ； 一氧化 ； 觸媒 ； 填充床 ； XRD

並列摘要

Unburned carbon from flue gas was oxidized to produce carbon monoxide (CO) in the presence of higher temperature and oxygen (O2). CO is an effective reducing gas for α-Fe2O3 catalyst to remove nitrogen monoxide (NO). A research to simultaneously remove NO and carbon by α-Fe2O3 packed bed was conducted. Five different parameters - temperature, NO influent concentration, α-Fe2O3 dosage, carbon dosage and O2 influent concentration - were tested, and active carbon was used to simulate the unburned carbon in flue gas. Under the carbon dosage of 2.0 g and α-Fe2O3 dosage of 3.0 g at NO influent concentration of 240 ppmv at 623 K, there was little NO reduction because of the lower temperature. Complete removal of NO, however, was achieved at 673 K, 723 K and 773 K, and the effectiveness of NO (mg) reduction appeared to rise with the increase in temperature. Results further study that the amount of NO reduction increased as NO influent concentration moved up within the range of 240-960 ppmv. When α-Fe2O3 dosage was more than 0.5 g, complete removal for NO was accomplished because of the sufficient active surface of α-Fe2O3. How much the CO would be produced relied on the dosage of the carbon used, and a greater dosage of carbon led to a greater reduction in the amount of NO. In respect of the influence of O2 influent concentration on NO reduction, the result indicated that the amount of NO reduction decreased as O2 influent concentration increased. Chemical reactions between NO/O2/α-Fe2O3/carbon were examined and verified by XRD (X-ray Powder Diffraction) analysis. According to the XRD analysis results, the main equation for the interaction mechanism was developed as follows:
C+1/2O2→1/2N2+CO2

並列關鍵字

Iron oxide ； unburned carbon ； nitrogen monoxide ； catalyst ； packed bed ； XRD

參考文獻

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