以微波輔助酸解處理MSWI飛灰之研究

Microwave-assisted Acid Degradation Treatment of MSWI Fly Ash

劉建中(Chien-Chung Liu)

指導教授 ： 章裕民

國立臺北科技大學/工程學院/工程科技研究所/博士(2013年)

https://doi.org/10.6841/NTUT.2013.00212

摘要

我國都市廢棄物之處理係以焚化處理為主，衛生掩埋為輔。都市廢棄物焚化爐所產生之飛灰所含之重金屬(尤其是鉛)及戴奧辛等有害物質含量常超過法規標準，必須被視為有害廢棄物處理。目前多以固化/穩定化加上衛生掩埋方式進行最終處理，對掩埋場容量造成極大負荷，也影響垃圾零廢棄政策推行。本研究係以微波輔助酸解方法一併削減飛灰中兩種有害物質(戴奧辛與鉛)，使焚化飛灰達無害化之目標，以利後續再利用。
微波酸解法具備均勻加熱、反應快速、低耗能及有效分解有害物質之特點。本研究採集台灣北部某大型都市垃圾焚化廠產出之飛灰及反應生成灰檢測分析其物化基本性質，另針對反應生成灰部分採用微波酸解法處理。本研究利用混合強酸H2SO4 (17.8M)之高沸點及HNO3(15.6M)之強氧化力特性，在固定微波功率600 W、固液比1/10之條件下、以不同處理時間及溫度進行實驗。研究結果顯示隨著作用時間愈長及溫度增加，處理後飛灰中之鉛TCLP溶出濃度呈現下降趨勢，尤其反應初期之削減效果相當顯著。在溫度433°K、時間16分鐘條件下，飛灰中鉛的TCLP溶出削減率達98.5％，即由原飛灰之46.2mg/l降為0.69mg/l，已低於台灣法規標準值(5 mg/L)。另以數值迴歸方式建立重金屬鉛TCLP削減效率之關係式為η(%)= 1-exp〔-30•t•exp (-2,210/T)〕。此式可應用在不同微波酸解作用時間及溫度條件下，快速估算飛灰中鉛TCLP溶出濃度削減效率(η)，以利選擇最經濟有效的操作條件，使得處理後飛灰符合法規標準。採用同樣之混合酸及微波功率，但選擇較高之固液比1/20，結果顯示在微波溫度160℃、處理時間30分鐘時，PCDDS/FS毒性當量濃度已降至0.00047 ng-I-TEQ/gdw，破壞去除率達99.94%以上，表示微波酸解處理法同樣對飛灰中之戴奧辛有極佳之破壞去除效果。
本研究以規模為100噸/日之微波酸解處理廠為基礎，搭配後續2段式水洗方式，其處理成本為6,877元/噸。雖較固化法處理成本3,758元/噸及2段式水洗法之3,939元/噸為高，但較熔融法10,049元/噸為低。微波酸解處理法最大優點為飛灰中主要的有害物質重金屬鉛及戴奧辛可被有效削減。處理後之飛灰可達無害化，有利於資源再利用，值得後續工程上評估應用。

關鍵字

微波酸解 ； MSWI ； 鉛 ； 戴奧辛 ； 飛灰

並列摘要

The refuse disposal strategy of Taiwan has adoped incineration as the primary method of treatment with landfills as supplement. Fly ash discharged from municipal solid waste incinerators (MSWI) was classified as hazardous waste because the leashing of heavy metals (especially Pb) and the content of PCDDS/FS are usually over the regulation limits, so it was majorly treated by Solidifition/Stabilization method, after that sent to the landfills for final disposal. Such way will caused the serious loading of limited landfills capacity and also affected the implementation of Zero Waste Policy. This study fouced on using the microwave-assisted acid degradation treatment (MDT) to reduce the hazardous materials (Pb and PCDDS/FS) simultaneously. The fly ash after MDT will be harmless and easily be resused.
Microwave-assisted acid degradation treatment has the advantages of uniform heating, quick reaction, low power consumption and effect reduction of hazardous materials. The fly ash (FA) and reaction ash (RA) used in this study were sampled separately from a domestic large-scale MSWI in northern Taiwan. They were tested by physical and chemical properties but only the RA was used for MDT test. The MDT method usesd an acid combination of H2SO4 (17.8M) for its high boling point and HNO3 (15.6M) for strong oxidation power, and tested with different reaction time and temperature in the same conditions of solid/liquid ratio (1/10) and 600W. It is found that the TCLP-extractable concentration of Pb will decrease with the increases of both treatment time and temperature, especially the reduction efficiency is significant in the early time of reaction. In the case of treatment temperature of 433°K, the reduction efficiency can reach 98.5％ after treatment time of 16 minutes. It is equivalent to the TCLP-extractable lead concentration of 46.2 mg/L in raw fly ash is down less than 0.69 mg/L, which is very lower than the hazardous regulation limit in Taiwan (5.0 mg/L). This work took the experimental data for correlation, and obtained the correlation equation between reduction efficiency and treatment time and temperature with a square correlation coefficient of 0.9401 as following: η(%)= 1-exp〔-30•t•exp (-2,210/T)〕. This equation can be used to estimate the reduction efficiency (η) for different temperature and time by the MDT in order to choose the effective operating conditions that make sure the fly ash after treatment is below the legal limits. The toxic equivalent concentration of PCDDS/FS has dropped to 0.00047 ng-I-TEQ/gdw (reduction efficiency is 99.94%) after MDT with the same test conditions above but higher solid/liquid ratio (1/20), which means that the MDT also get good reduction efficiency for PCDDS/FS in fly ash.
In this study, on the basis of 100 tons / day for MDT plant scale, with a subsequent two-stage washing units, the treatment cost is 6,877 NTD / ton. The fee is higher than solidifition method (3,758 NTD / ton) and two-stage water washing method (3,939 NTD / ton), but lower than the melting technology (10,049 NTD / ton). The most important advantage of MDT is that the major hazardous substances of heavy metals and PCDDS/FS in fly ash could be reduced effectively so that the fly ash after treatment will be harmless and beneficial for recycling and utilization. It is worthing on the follow-up application.

並列關鍵字

Microwave-assisted Acid Degradation ； MSWI ； Pb ； Dioxin ； Fly Ash

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