本研究主要目的為建立工業爐內單燒高爐氣(BFG)之燃燒技術，以降低穩焰所需的輔助燃料使用量，對於補充目前煉焦爐氣(COG)短缺，因而減少外購高價能源成本極有幫助。研究內容主要分為四部分： (1)理論分析單燒和混燒高爐氣的熱能轉換特性，(2)實驗分析鈍氣對噴流擴散火焰的影響， (3)理論分析鈍氣對噴流擴散火焰的影響，(4)現場鍋爐實驗。
第一部分為理論分析單燒和混燒高爐氣的熱能轉換特性，探討參數包含燃料使用量、化學計量空氣需求量、絕熱火焰溫度與煙道氣排放量。結果顯示：在化學計量比且無預熱條件下，單燒高爐氣需要大量燃氣才能達到預定產熱。以煉焦爐氣混燒高爐氣，燃氣量減少，但燃燒空氣量卻增加，而絕熱火焰溫度隨之上升。當單燒高爐氣時，煙道氣富含高爐氣本身的不可燃氣，故其體積流率高；若以煉焦爐氣混燒高爐氣，煙道氣體積流率隨高爐氣減少而降低。此外，並探討加入10%的過剩空氣與0.1MW的預熱條件下，製程氣燃燒特性的變化。
第二部分以實驗分析鈍氣對噴流擴散火焰的影響，在雙環同軸噴流燃燒器中，內環通入甲烷鈍氣混合氣，外環則通入空氣，所選用的鈍氣為氮氣或二氧化碳。甲烷噴流擴散火焰在流速低時為層流火焰，焰色為明亮的黃色，隨燃氣出口流速增加，火焰長度變長。甲烷噴流擴散火焰在內環流速較低時，加大外環空氣流速，火焰破孔後直接被吹熄，不會產生上飄。若增加鈍氣比例，火焰高度會降低，當氮氣比例超過70%或二氧化碳比例超過80%時，火焰無法點燃。隨著鈍氣比例增加，火焰破孔點及熄滅點所對應之外環空氣流速皆較低。在相同鈍氣比例下，內環噴流速度越大，火焰破孔點所對應之外環空氣流速會越低。
第三部分為理論分析鈍氣對噴流擴散火焰的影響，利用氣態燃燒理論方法，推導其理論。結果顯示：在甲烷噴流擴散火焰中，邊界層厚度隨軸向位置增加而增加，徑向速度與軸向速度則隨軸向位置增加而減低；氣體溫度、二氧化碳及水氣濃度皆在火焰面為最大值，並隨著徑向位置遠離火焰面而下降。隨著鈍氣比例增加，邊界層厚度、火焰長度與火焰半徑皆越小；在火焰面上的甲烷濃度、水氣濃度及氣體溫度皆較小。
第四部分為現場鍋爐實驗，主要利用鍋爐系統在正常運轉高負載(70%及60%)以及冷爐起爐低負載(50%及40%)情況之下，分析單燒和混燒高爐氣的熱能轉換特性，訂定高爐氣所需的最低輔助燃料使用量，評估單燒高爐氣之操作條件與時機。固定鍋爐負載即固定燃料之總產熱，隨著煉焦爐氣流率減少，高爐氣流率會增加。現場實驗中，排放的CO濃度相當低，而NOX隨煉焦爐氣流率減少而逐漸降低。由研究結果可知，無論高負載或低負載，調降煉焦爐氣流率，均無火焰不穩定（上飄或飄離）問題。此外，調降煉焦爐氣流率最低可至830 Nm3/hr，但基於安全因素，目前現場五部鍋爐只將煉焦爐氣輔助用量由原先3000 Nm3/hr降至2000 Nm3/hr，保守估計每年約可省下四千多萬元的能源成本效益。

Based on economical considerations, it is advantageous to develop the combustion technology of firing by-product gases without the support fuel for boilers in a steel mill plant. The research includes four parts: (1) theoretical analysis of individual firing and co-firing. (2) experimental study of the influence of inert gas on a jet diffusion flame. (3) theoretical analysis of the influence of inert gas on a jet diffusion flame. (4) test run in the boiler.
The first part is to analyze the combustion characteristics of individual firing and co-firing. The results show that the BFG gas volume flow rate is greater when firing individually than when firing BFG with a support fuel if a prescribed heat output is to be reached. A smaller air volume flow rate, a lower adiabatic flame temperature and a lower thermal efficiency are also found for the former case. The higher volume flow rate is necessary for the reason that BFG contains a large amount of inert gases. Additionally, the combustion characteristics of firing BFG individually or in combination with COG were discussed under the operating conditions of 10% excess air and/or 0.1MW preheat.
The second part is an experimental study of the influence of inert gas on a jet diffusion flame. The inert gas is carbon dioxide or nitrogen. The flame height is increased linearly with the jet velocity. Increasing the concentration of inert gas in the central jet decreases flame height and the flame color changes from yellow to blue. When the concentration of nitrogen in the central jet is more than 70% or when carbon dioxide is more than 80%, the flame can not be ignited. The critical outer airflow velocity at which broken flame or blow-out decreases with increasing concentration of inert gas in the central jet. At the same concentration of inert gas, the critical outer airflow velocity at which broken flame results is lower when the central jet has a greater exit velocity.
The third part is theoretical analysis of the influence of inert gas on a jet diffusion flame. The results show that in methane jet diffusion flame, the thickness of boundary layer increases with distance from the axis. Radial and axial velocity components decrease with distance from the axis. Besides, the gas temperature, CO2 concentration and steam concentration are maximal at the flame front. These quantities also decrease at a higher radial distance from the flame location. The thickness of boundary layer, flame height, and flame radius decrease when the inert gas concentration increases.
The fourth part is the test run of boiler. The experimental results obtained from an industrial boiler fired with BFG in combination with COG show that irrespective of a higher or lower boiler load, with gradually decreasing amount of COG, flame instability (lift-off and blow-out) did not occur and brought CO emission is low. In addition, a decrease in the amount of COG brought about a reduction in NOX emission. The minimal COG flow rate can be 830 Nm3/hr. However, based on safety consideration, the COG flow rate of five boilers was only decreased from 3000 to 2000 Nm3/hr. The cost was cut down about 40 million NTD per year.

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