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研究生:林怡潔
研究生(外文):Yi-ChiehLin
論文名稱:添加煙道氣體於預混富氧甲烷火焰之效應
論文名稱(外文):Effects of Fluegas Addition on the Premixed Oxy-Methane Flames
指導教授:趙怡欽
指導教授(外文):Yei-Chin Chao
學位類別:碩士
校院名稱:國立成功大學
系所名稱:航空太空工程學系碩博士班
學門:工程學門
學類:機械工程學類
論文種類:學術論文
論文出版年:2012
畢業學年度:100
語文別:中文
論文頁數:72
中文關鍵詞:富氧燃燒煙道氣體火焰結構層流火焰速度
外文關鍵詞:Oxy-fuelOxy-combustionFluegasFlame structureLaminar burning velocity
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  因為能源議題與環保意識崛起,富氧燃燒(oxy-combustion)在近十年來受到廣泛討論研究,將燃燒後排放的二氧化碳引入迴流至鍋爐中燃燒結合二氧化碳捕捉的概念,因而成為目前最為矚目的發電技術之一。因此,新型碳回收富氧燃燒發電設備以及如何以現有的發電設備重新翻修適用於富氧燃燒即成為近來重點研究方向。因為迴流用以降低溫度的二氧化碳與氮氣體物理特性不同,許多文獻皆探討富氧-粉煤燃燒的熱傳與傳遞特性與空氣-粉煤燃燒特性進行比較,如:二氧化碳輻射熱傳效率高於氮氣以及火焰傳遞速度慢且有點火時間延遲等現象對於整體效率的影響。然而,當回流煙道氣中二氧化碳與水分參與燃燒中反應時不僅僅式熱效應的影響,兩者皆會改變火焰反應路徑。但是這方面煙道氣體迴流對富氧火焰之化學效應相關研究卻甚少。
  因此本研究藉由數值模擬方法分別以CO2、H2O氣體以及煙道氣(Fluegas)(33%CO2+67%H2O)添加於富氧甲烷討論對火焰燃燒特性影響以及在數值模擬中利用假設不參與化學反應之惰性氣體CO2(A)、H2O(A)以及煙道氣Fluegas(A)添加於富氧甲烷分別比較化學效應對火焰結構造成影響。對於預混火焰來說,最關鍵的參數即為層流火焰速度其代表了火焰燃燒的強度,層流火焰速度值為判斷燃燒特性很重要的參考依據,因此,本論文也將利用圓錐形穩駐火焰量測層流火焰速度並且與數值結果比較。比較其結果顯示,數值計算結果與實驗結果皆誤差範圍皆為10%內,最低誤差值也僅為1.5%之誤差。絕熱火焰溫度計算與層流火焰速度(Laminar flame velocity)之結果由大至小皆分別依序為迴流氣體N2、H2O、煙道氣(Fluegas)以及CO2。而迴流氣體H2O(A)、Fluegas(A)以及CO2(A)之絕熱火焰溫度計算結果與迴流氣體H2O、Fluegas以及CO2之值並無明顯差異;層流火焰速度值則有明顯差異,顯示其反應速率改變影響火焰速度值。觀察火焰溫度以及物種(species)濃度分佈可以發現不同氣體之火焰位置皆有偏移現象,自由基濃度也明顯差異,比較其化學效應影響可以發現甲烷消耗的反應步驟由原本反應式R53(H+CH4CH3+H2)轉變為R98(OH+CH4CH3+H2O)為主要反應步驟。其主要原因皆是由於迴流氣體化學效應造成反應路徑改變,進而影響反應速率以及自由基和物種濃度,火焰速度靈敏度分析結果皆顯示主要火焰速度之反應步驟為R38(O2+HóO+OH)。

Owing to the rising of the environmental protection awareness, oxy-enriched combustion in the last decade has been widely discussed. The concept of combined post-combustion emissions (Flue gas) recycling with carbon dioxide capture (CCS) has been the most attentive scheme for power plants in present. Thus, how to retrofit traditional coal-fired power plants for oxy-fuel combustion has become the main focus for research in recent years.
The oxy-fuel combustion using recirculated carbon-dioxide as diluents may behave differently with the traditional air combustion with nitrogen as the diluents. The difference in physical chemical properties between carbon-dioxide and nitrogen may result in different combustion and flame phenomena. Many papers have focused on comparing the flame heat transfer, flame stability and ignition delay characteristics between air-coal and oxy-coal combustion. However, the content of carbon-dioxide and steam in the flue gas not only has thermal effects on combustion, but also changes reaction path in the flame. However, the chemical effects on oxy-fuel combustion have not been intensively studied and discussed so far. Thus, in this study we focus on the characteristics of chemical effects of the recirculated flue gas containing CO2 and H2O on the oxy-fuel combustion by adding CO2, H2O gases and Fluegas (33%CO2+67%H2O) into oxygen/methane flame separately using numerical simulation and comparing with the results using fictitious chemically-inert gases CO2(A), H2O(A) and Fluegas(A) for further analysis of the chemical effects on flame structure and flame characteristics. Laminar burning velocity is the crucial parameter for premixed flame, which is the major flame characteristic expressing the burning intensity. Therefore, in this study we first use a conical flame to measure laminar flame speed for comparison and validate the numerical simulation results. The results show that the discrepancy is within 10%, and the minimal error is only within in 1.5%.
  The simulation results show that adiabatic flame temperature and laminar burning velocity gradually decreases with increasing concentration of added gas N2, H2O, Fluegas and CO2 into oxygen/methane flame separately. In contrast, the numerical results of adiabatic flame temperature of the added the fictitious inert gas CO2(A), H2O(A) and Fluegas(A) as compared with the real gases H2O, Fluegas and CO2 have little difference. On the other hand, the laminar burning velocity has significant variation, it indicates that chemical effects of the recirculated gases do change the combustion characteristics significantly in terms of the burning velocity.
  By observing the resultant flame temperature and species concentration profiles one can identify that the flame location shifts, and the concentration profile of major chemical reaction radicals varies, indicating the change of flame structure and flame chemical reaction paths. The dominant initial consumption reaction step of methane shifts from R53 (H+CH4CH3+H2) to R98 (OH+CH4CH3+H2O) when nitrogen is replaced by the recirculated gases. It is because the chemical effects of the recirculated gases changes the flame reaction pathway, and further affect reaction rate, species and radical concentrations. Sensitivity analysis of the burning velocity shows that the important reaction step is R38 (O2+HóO+OH).

摘要 i
Abstract iii
誌謝 v
目錄 vi
表目錄 viii
圖目錄 ix
符號表 xi
第一章緒論 1
第二章文獻回顧與研究動機 4
2-1文獻回顧 4
2-2 研究動機與目的 10
2-3研究方法 10
第三章實驗方法與設備 12
3-1氣體供給設備 13
3-2燃燒器設備 13
3-3層流火焰速度量測 14
3-4紋影法 (Schlieren)與影像處理 14
3-5校正彎曲(curvature)及拉伸(stretch)效應 15
第四章數值方法 18
4-1 Equil-code 18
4-2 Premix-code 18
4-3 化學反應機構 19
第五章結果與討論 21
5-1絕熱火焰溫度計算 21
5-2層流火焰速度 21
5-2-1數值計算結果 22
5-2-2實驗與計算結果比較 22
5-2-3火焰尖端之開口現象 23
5-3層流火焰速度靈敏度分析 24
5-4火焰結構分析 24
5-4-1物種濃度分佈比較 24
5-4-2主要物種反應速率比較 26
第六章結論 33
6-1結論 33
6-2未來工作 34
參考文獻 35

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