| 摘要: | 本研究針對水泥廠進行調查，對煙道氣之汞排放特性進行探討，並採集其製程物料用以研究循環經濟下，水泥廠接收不穩定汞濃度之再生物料使用，於此情形下之汞質量流布與平衡。調查之水泥廠兩排放管道煙道汞濃度皆超過目前草案標準(50 µg/m3)，而煙道氣的汞來源以原物料為主，因此了解水泥廠汞輸入至關重要。調查之水泥廠汞輸入主要以的鐵渣為主(40.9%)，石灰石(23.0%)次之，再者為矽砂(13.4%)，再生物料中的燃煤飛灰(8.84%)與水洗飛灰(5.67%)的佔比也是相當的高。在原物料與再生物料比率及其汞流率佔比，可見再生物料單位汞含量(0.2667 mg/kg)遠高於原物料(0.0652 mg/kg)，由此可見灰(鐵渣、煤灰、水洗灰)等再生物料的使用，改變了水泥廠汞輸入結構；中間產物的生料磨後集塵灰含汞量最高(達19.7 mg/kg)，並以同為集塵灰的煤磨後集塵灰濃度第二(達14.7 mg/kg)，混合生料汞含度則為2.05 mg/kg，由此可見三個中間產物的富集能力強;而水泥廠汞輸出主要以煙道氣之汞輸出為主，其輸出汞質量流率為16.34 g/hr，佔總輸出之98.8%，而熟料輸出汞質量流率為0.16 g/hr，佔總輸出之1.1%。汞排放係數(Mercury emission factor, MEF) 指單位時間或單位產量內排放的汞量，可用於風險評估。由文獻蒐集資料發現水泥業煙囪MEF值介於1.8 ~ 253 mg Hg/ton clinker，本研究之生料磨煙囪其排放係數為165 mg Hg/ton clinker相對較高的，而煤磨煙囪排放係數則為6.6 mg Hg/ton clinker，其值相對較低。本研究之質量平衡比率為130%，雖然說是偏高但介於70 ~ 130%屬於可以接受的範圍。循環經濟對水泥製程中的汞排放有重大影響，水泥業的再生物料使用量逐年上升，而水泥業汞排放濃度與排放係數也有逐漸上升之趨勢。調查高汞含量之樣品發現，汞以化學吸附方式吸附於中間產物，而中間產物經過高溫後再次釋放至煙道中並以元素汞形式排放至大氣中。對於汞排放濃度增加，廠方可以增加防制設備或停止回流水泥廠產生之飛灰，政府目前對排放濃度之改善政策以降低再生物料汞含量為主，但本研究認為可能需與美國政策相同，對於進料之汞含量限制，降低汞排放濃度以達排放標準。;This study delves into the mass flow and balance of mercury in a cement plant, and investigates the emission characteristics of mercury from flue gas. Additionally, the causes of high mercury concentration in solid sample due to the implementation of circular economy policy are studied. In short, the study investigates mercury flows through out the cement plant, particularly as the plant receives fly ash with unstable mercury concentrations as recycled material. The research reveals that the primary mercury input in the cement plant investigated is iron slag (40.9%), followed by limestone (23.0%) and silica sand (13.4%). The contributions of coal fly ash (8.84%) and washed fly ash (5.67%) are also significant. The data on the mercury flow rate from raw material and recycled material indicate that mercury content of recycled material (0.2667 mg/kg) is much higher than that of raw material (0.0652 mg/kg). The study shows that the use of recycled materials, including iron slag, coal ash, and washed fly ash, has altered the structure of mercury input in this cement plant. This study also demonstrates that intermediate products of the cement production process have a strong ability to enrich mercury, with the concentration of mercury in the dust collected in raw mill reaches 19.7 mg/kg, followed by 14.7 mg/kg in dust collection in coal mill, and 2.05 mg/kg in raw meal. The mercury output of cement plant is mainly via flue gas, with the mercury mass flow rate of 16.34 g/hr, accounting for 98.8% of the total output, while the clinker output mercury mass flow rate is only 0.16 g/hr (1.1%) of total output. The mercury emission factor (MEF) refers to the amount of mercury emitted per unit clinker produced. Previous studies indicate that the MEF value ranges from 1.8 to 253 mg Hg/ton clinker. The MEF of the raw mill stack in this plant is 165 mg Hg/ton clinker, while the MEF from coal mill stack is 6.6 mg/ton clinker. The mass balance ratio of this study is 130%, which is within the acceptable range (70 ~ 130%). The circular economy has a significant impact on mercury emissions in the cement manufacturing process. The amount of recycled materials used in the cement industry is increasing year by year, and the mercury emission from the cement industry is also gradually increasing. Investigation of solid samples indicates that the mercury was chemisorbed in intermediate products, which were released again into the flue gas at high temperatures and emitted into the atmosphere in elemental form. Overall, this study indicates that we should carefully examine all the materials applied and enhance the performance of APCDs to reduce mercury emission. |
