| 摘要: | 汞對於動物、植物、和人體健康都有很大的危害，且為全球性第一級之污染物質，本研究以中石化安順場受污染土壤為對象，經文獻蒐集後選擇以熱處理法(熱脫附法)對於目前中石化安順廠址之高濃度汞污染土壤有快速、處理量大、效率高等優點，先透過實驗室批次試驗以及連續熱脫附模組，再評估不同操作參數下對土壤中汞之去除效率做探討及比較。實驗室批次試驗結果顯示操作溫度高於500oC時土壤殘餘濃度均可達到法規管制標準值20 mg/kg以下，且隨著操作溫度的增加，去除效率也提升至接近100%；之後將操作參數以500、600、700及750oC之條件應用於連續式熱脫附模組中，於處理量為2、2.5及3 kg/hr之條件下(停留時間分別為33、26及22分鐘)，於700oC處理後之土壤皆低於管制標準值，且去除效率皆可達97.88%以上；此外為避免二次污染問題，熱脫附模組後方搭配一套空氣污染防制設備，其流程為：袋濾式集塵器、驟冷塔及多層床式活性碳吸附塔串聯以去除模組產生出來之高濃度汞氣流，實驗結果也發現，袋式集塵器可有效捕集廢氣中99%以上粒狀污染物，減輕後方防制設備之負擔，驟冷塔除了冷凝水氣以外，更可有效捕集氣流中汞及其化合物，並發現元素態汞沉澱，最後以多層式活性碳床把關，實驗結果顯示尾氣通過多層活性碳床氣流中汞濃度皆低於我國之排放標準50 μg/Nm3，且透過實驗室活性碳吸附貫穿試驗，建議以每天更換再生一層活性碳床之操作條件，可確保尾氣之排放濃度符合法規標準。;Mercury (Hg) is one of the hazardous metals for animals, plants and human beings and has been listed as the first priority toxic substance in the world. In this study, the mercury-contaminated soil was collected from An-shun site in Tainan and was sieved to remove the branches, rocks and bricks for experimental tests. Thermal desorption is experimentally evaluated for the effectiveness in removing Hg from contaminated soil, because it has advantages including high treatment capacity and high removal efficiency. First of all, the experimental tests were conducted with a batch-type laboratory-scale thermal desorption system. In order to evaluate and compare the removal efficiencies, the experimental tests were performed at different operating conditions including temperature and the type of carrier gas. The results indicate that when the operating temperature is above 500oC, the Hg content of the treated soil concentration is below the Taiwan EPA criteria (20 mg/kg) and Hg removal efficiency increases with increasing temperature. The continuous thermal desorption system was operated at 500, 600, 700 and 750oC, while the treating capacity was controlled at 2, 2.5 and 3 kg/hr (retention time: 33 min, 26 min and 22 min), respectively. The results show that the removal efficiency reaches 97.88% at the operating temperature of 700oC and the residual concentration in treated soil could also meet the criteria of 20 mg/kg. Finally, in order to avoid the secondary pollution, a series of air pollution control devices (APCD) consisting of a baghouse, a quench tower and a multilayer activated carbon adsorption bed are designed and adopted. Experimental results indicate that the baghouse could effectively remove 99% particulate matter and reduce the loading of subsequent APCDs. The quench tower could not only condense the water vapor but also capture the Hg and its compounds, with significant accumulation of mercury drop in the chilled water. As the off gas passes through the activated carbon adsorption bed, mercury concentration in off-gas is well below the emission standard promulgated by Taiwan EPA (50 μg/m3). Results obtained from activated carbon adsorption test indicate that the replacement of AC beds should be maintained at 1 layer/day to ensure the Hg concentration in off gas meet the emission standard of 50 μg/Nm3. |
