使用天然氣的微富氧燃燒之實驗研究

Abstract

本實驗研究目的是探討微富氧空氣的氧濃度變化對燃燒爐之加熱速度、煙氣、溫度分佈和燃料消耗量的影響。燃燒爐有實驗室與先導型二種尺度。每個尺度的燃燒爐都分別做加熱試驗和固定爐溫試驗，所使用的燃料是天然氣(CH4:82%, C2H6:2.6%, C3H8:1.8% and CO2:13.6%)，實驗的氧濃度條件分別為21%、24%、26%、28%以及30%；而過剩空氣係數則控制在可以達到完全燃燒反應的範圍內。由實驗結果顯示，於實驗室與先導型尺度燃燒爐試驗都會因當氧濃度增加可以縮減加熱時間並且減少燃料消耗量而有節能的效果，這是由於減少富氧空氣中不參予反應的氮氣所致。而在實驗室尺度試驗中，氮氧化物的生成會隨著氧濃度的增加而急遽增加，同時也發現氮氧化物的生成在高氧濃度的狀態下對過剩氧是極為敏感的；但是在先導型尺度試驗中，氮氧化物的生成量則是幾乎相同的，這是由於其燃燒器無法將燃料與空氣混合很好所致。此外，在實驗研究中發現於實驗室與先導型尺度試驗，二氧化碳的濃度皆會隨著氧濃度的增加而呈線性提高。在實驗室尺度固定爐溫試驗中，在溫度分佈方面，氧濃度越高溫度分佈越不均勻，這是由於熱對流變弱所造成。另外在先導型尺度固定爐溫試驗中，發現輻射熱通量會隨著氧濃度增加而增加。因此由本論文實驗結果可確認富氧燃燒不僅能減少能源的花費，而且可提升生產效率和產品產量。

The experimental investigations were aimed at studying the influence of oxygen-enriched air on the heating speed, emissions, temperature distributions and fuel consumption of the furnaces, which were Lab-Scale and Pilot-Scale, respectively. The experiments for each type of furnace were divided into two parts: the heating test and the fixed furnace-temperature test. The fuel used was the natural gas (CH4:82%, C2H6:2.6%, C3H8:1.8% and CO2:13.6%), and there were five different oxygen concentrations, which are 21%, 24%, 26%, 28% and 30%. The excess air ratio was controlled such that it could achieve complete combustion in the experiment. Based on experimental results, the increase of oxygen concentration led to the faster heating speed and less fuel consumption in both Lab-Scale and Pilot-Scale tests because less energy was used to heat up the less amount of inert gas (N2) in the oxygen-enriched air. The NOx emission increases sharply as the oxygen concentration increases in the Lab-Scale experiments. Moreover, the NOx emission was more sensitive to excess oxygen at higher oxygen concentration condition. However, the total amount of NOx emissions was almost invariant as the oxygen concentration increased in the Pilot-Scale experiments. This is due to poor mixing of oxidant and fuel of burner. The CO2 concentration increased linearly with the oxygen concentration in both Lab-Scale and Pilot-Scale heating tests. The temperature distributions became more non-uniform as increasing oxygen concentration in the Lab-Scale fixing furnace-temperature test, because the convection heat transfer was weakened. The radiation heat flux increased with oxygen concentration in the Pilot-Scale fixing furnace-temperature test. Based on the experimental results of this study, the oxygen-enriched combustion can save energy, and elevate manufacture efficiency and product quality.