農業廢棄物焚化溫度對PAHs廢氣產生之影響

Abstract

國內農業廢棄物非常多，有些採用資源回收方式處理，有些則採用焚化方式處理。雖說焚化並不是最好的處理方式，但卻是最快的處理方式。在我們的社會上還是常常看見露天燃燒農作廢棄物、燃燒病死動物以及燃燒農業廢塑膠等等，但所排出的廢氣到底對環境污染有多大？該如何焚化才能降低污染排放？則是本論文想要探討的課題。 本論文針對不同的農業廢棄物進行焚化，實驗結果顯示，廢棄物中含有苯環的物質較易生成多環芳香碳氫化合物(PAHs, polycyclic aromatic hydrocarbons)，長碳鏈的化合物比短碳鏈的化合物更容易生成PAHs，正十六烷排放PAHs約正己烷的8-9倍，病死動物中可能含有很多的水份，焚化後PAHs排放反而比較少，每克病死豬肉焚化約排放16種PAHs 104微克。值得注意的是在我們生活中常看到露天焚化農作廢棄物，也會排放多量的PAHs，約病死豬焚化的10-45倍。 苯環需要到900℃以上才能有效打開，但900℃以上的焚化爐不管在設備上，或耗燃油上都必需花費較多的經費，倘若考量在低成本的焚化設備下處理，則400-500℃是比較適合的處理溫度，700-800℃反而會容易造成PAHs大量生成，故建議農業廢棄焚化溫度應設定在400-500℃比較恰當，不過其他廢氣的排放因素亦應一併考量。

Agricultural wastes are abundant in Taiwan. They are either recycled as a resource or incinerated in a small portion. Although incineration is not the ideal processing method, yet it is the most rapid way. In the field, we can often observe the incineration of agricultural wastes, dead and sick animal carcasses, agricultural plastics, etc. What impact does the waste gas has on the environment? How to incinerate in order reduce waste gas emission? This is the main discussion topic in this thesis. This thesis focuses on the incineration of different agricultural wastes and the experimental results. Benzene-related structure in the waste is relatively easy to turn into PAHs after incineration. Long-chain compounds are relatively easier to form PAHs as compared to short chain compounds. The PAHs amount emitted by burning hexadecane is 8 to 9 times of burning hexane. Dead and sick animal carcasses contains large amount of water, thus emit less PAHs after incineration. Burning each gram of rear-leg meat produces 16 kinds of PAHs, in a total amount of 104 μg. It is interesting to note that in our daily life, we can observe in-the-wild incineration process of agricultural wastes where PAHs are emitted in a large amount, which is 10 to 45 times of emission by burning rear-leg meat. Benzene structure can be opened at 900℃, yet a 900℃ incinerator is expensive and the energy consumption is high. If a low cost incinerator is considered, then incineration at 400-500℃ is more suitable. 700-800℃ incineration, on the other hand, generates more PAHs. Therefore, we recommend the incineration temperature of agricultural wastes to be set at 400-500℃ where the emission of other waste gases are considered as well.