焚化飛灰再利用情境之特性與生命週期評估

Abstract

在現今全球人口增加的狀況下，都市廢棄物的產生隨之漸增，伴隨而來的垃圾處理技術也須進行考量，自從民國80年開始，政府開始推廣以「焚化為主，掩埋為輔」的垃圾處理政策，以減輕垃圾掩埋的負擔，但焚化廠還是會產生殘渣，包含飛灰及底渣，其中飛灰被定義為有害廢棄物，更必須妥善處理飛灰，而我國最常使用技術為固化掩埋，反而更增加掩埋場的負擔，因此近幾年台北市政府開始推動焚化飛灰再利用的方案，鼓勵各焚化廠將飛灰妥善再利用，例如再利用成水泥、紅磚、鹼劑、飛灰熔融處理製成骨材等，不過這些再利用技術十分新穎，飛灰添加後會造成製程環境衝擊增大，在本研究目的主要探討目前國內外常用焚化飛灰處理及再利用技術之環境衝擊與成本，評估最合適的飛灰再利用技術。 本研究探討飛灰處理流程為經飛灰水洗程序後，接著四個情境，1)固化掩埋、2)再利用成水泥、3)再利用成紅磚、4)再利用成鹼劑於華爾滋法，因此本研究分為兩個階段，第一部分為飛灰水洗前後進行實驗分析重金屬成分，來了解水洗前後飛灰性質的差異，第二部分則比較飛灰處理及再利用流程的生命週期評估，盤查程序的資料透過實廠及文獻得到，並使用SimaPro生命週期評估軟體及衝擊評估IMPACT 2002+進行最後環境衝擊結果的闡述。在實驗結果部分，發現雖然水洗後飛灰毒性較為穩定，但水洗後飛灰會有重金屬富集現象；而在生命週期評估比較後結果，以情境四衝擊最低，其次為情境三、情境一，衝擊最高則是情境二，主因為情境四中回收氧化鋅效益過高，而使此情境接近零衝擊。 未來隨著人口增加，土地利用不足等問題，在焚化飛灰再利用的議題越顯重要，更需要其他飛灰再利用的研究進行探討，如其他經濟、社會層面的考量、飛灰重金屬再利用後溶出狀況，從環境衝擊角度來看，本研究可提供政府焚化飛灰再利用於環境衝擊層面的比較與考量，選擇飛灰再利用較佳的方案以作為政策。

As global population has increased, the generation of municipal solid waste has also increased and its treatment is a salient issue for many governments. Fly ash is a byproduct of solid waste incineration and is regarded as hazardous waste. Yet fly ash can be reused in cement, bricks, alkaline, aggregate sand other treatments. However, these fly ash reuse treatments might create higher environmental impacts. Therefore, the study aims to discuss the most common fly ash reuse and treatments and evaluate them by environmental impact and cost benefit analysis, to choose the better fly ash reuse treatment alternatives. This research discusses four kinds of fly ash treatments scenarios: 1) Landfill after solidification, 2) Reuse as cement, 3) Reuse as bricks, 4) Reuse as alkaline in Waelz process, and evaluates each in two parts. The first part experimental, which analyzed heavy metal composition before and after washing process. The second part is to evaluate fly ash reuse treatment by life cycle assessment. Inventory data were obtained from commercial operation factories and references, and LCA software SimaPro and environmental impact model IMPACT 2002+ were used to evaluate the outcome of LCA. It was found that although washed fly ash can stabilize toxic substances, it also can increase heavy metal concentration, In LCA portion, the highest impact scenario is scenario 2, second is scenario 1, third is scenario 3, the lowest impact is reusing as alkaline of the low impact of scenario 4 is due to the benefit from recycling zinc. Fly ash reuse treatment will be increasingly important and will require many considerations. In terms of environmental impact, this research aims to provide a holistic comparison between different fly ash reuse treatments to further recommendation of better fly ash reuse treatment.