| 摘要: | 瀝青混凝土拌合廠(瀝青拌合廠)經常是居民陳情異味及揚塵公害對象，本研究從污染源、受體及模式模擬三個方面探討瀝青拌合廠污染特性及暴露風險評估。當燃燒六號重油進行砂石乾燥的廢氣，經旋風分離器與袋式集塵器串聯處理後粒狀物、硫氧化物及氮氧化物的排放因子分別為0.0146公斤/公噸（砂石）、4.5669公斤/公秉(重油)、4.5701公斤/公秉(重油)；採用天然氣為燃料經旋風分離器與袋式集塵器串聯的粒狀物、硫氧化物及氮氧化物、揮發性有機物排放因子則分別為0.0236公斤/公噸（砂石）、1.1763公斤/千立方公尺(天然氣)、1.2080公斤/千立方公尺(天然氣)、0.0193公斤/公噸（砂石）。瀝青刨除料如以重油為燃料進行乾燥的廢氣，其粒狀物、硫氧化物及氮氧化物排放因子分別為0.0128公斤/公噸(再生骨材)、3.8319公斤/公秉(重油)、2.9797公斤/公秉(重油)；以天然氣為燃料排放因子則依序分別為0.0066公斤/公噸(再生骨材)、0.9781公斤/千立方公尺(天然氣)、0.9871公斤/千立方公尺(天然氣)及0.2925公斤/公噸(再生骨材)。
當燃料用六號重油改為天然氣，硫氧化物及氮氧化物的排放減量，以新料乾燥時分別為85.3%、95.7%；以瀝青刨除料乾燥則為69.4%、92.3%。比較將重油改用天然氣燃料成本差以及空污費減徵的單位產能成本減少新台幣2.3元/公噸（成本降低約0.12%）。刨除料乾燥以天然氣燃料產生廢氣經旋風分離器與尾氣燃燒室串聯處理後的揮發性有機物及異味削減率分別為53.8%、92.4%，由兩者削減效率不等顯示異味來源並非全由揮發性有機物所貢獻。瀝青刨除料乾燥以重油為燃料產生廢氣，經旋風分離器及尾氣燃燒串聯，廢氣中PAHs去除效率僅為18.67%，甚至部份PAHs成份出口濃度大於廢氣入口，主因是尾氣燃燒使用重油反而造成PAHs增加。本研究有兩廠製程相似且使用相同燃料時，排放因子的差異百分比範圍為-6.8%~60.6%，因此以它廠排放因子推估自廠排放量可能造成大誤差。
以ISC（Industrial Source Complex）模擬A工廠到達三個選定人口密集點的TSP、PM10、PM2.5、硫氧化物及氮氧化物與背景濃度加成後濃度分別為TSP 43.37~44.13 μg/m3、PM10 36.88~36.99 μg/m3、PM2.5 18.50~18.50 μg/m3、硫氧化物6.3~6.74 ppb、氮氧化物26.96~27.88 ppb，以上濃度都未超過我國環境空氣品質標準。TSP最大落地濃度發生位置距離Ａ工廠大門120公尺，硫氧化物、氮氧化物則為1161公尺。
以A工廠排放管道異味達標準值的2000模擬三個選定人口密集點不同樓層異味，濃度範圍分別為1.65 ~12.67、2.04~19.79、1.84~16.18，且分別在20、16、18樓的異味濃度已大於10，使民眾明顯感受Ａ廠異味，顯示雖然當工廠已將廢氣處理至符合異味標準時，仍有遭民眾陳情的可能。異味濃度最大值發生位置距離大門約63公尺，高度75公尺處（相當25層樓）。最後，本研究關切瀝青混凝土拌合過程以天然氣為燃料排放的苯吡（Benzo(a)Pyrine, BaP）健康風險，經推算在三個選定人口密集點居民暴露族群苯吡（BaP）終生致癌風險分別為2.08×10-5、8.91×10-6、3.96×10-6，屬於一般可接受風險範圍。
;Hot mix asphalt (HMA) is often the target of complaints by local residents for the odor and fugitive dusts. This study investigated emission characteristics and exposure risk assessment of HMA from the aspects of source, receptor, and model simulation.
For the sandstone drying of HMA plants by using No.6 heavy oil, the emission factors of TSP, SOx, and NOx from waste flow after being treated by an integration of cyclone separator and bag filters are 0.0146 kg/ton (sandstone), 4.5669 kg/kl (No.6 heavy oil), and 4.5701 kg/kl (No.6 heavy oil), respectively. When heavy oil was switched into natural gas for the same pollution control system, the emission factors of TSP, SOx, NOx, and VOCs are 0.0236 kg/ton (sandstone), 1.1763 kg/km3 (natural gas), 1.2080 kg/ km3 (natural gas), and 0.0193 kg/ton (sandstone), respectively. For the reclaimed asphalt pavement (RAP) of the same pollution control system by using No.6 heavy oil, the emission factors of TSP, SOx, and NOx are 0.0128 kg/ton (RAP), 3.8319 kg/kl (No.6 heavy oil), and 2.9797 kg/kl (No.6 heavy oil), respectively. The emission factors of TSP, SOx, and NOx are 0.0066 kg/ton(sandstone), 0.9781 kg/km3(natural gas), and 0.2925 kg/km3(natural gas), respectively, when heavy oil was switched into natural gas for the same pollution control system.
When switching No. 6 heavy oil into natural gas for the fuel of sandstone drying, the emission reductions of SOx and NOx were 85.3% and 95.7%, respectively; and 69.4% and 92.3% for RAP, respectively. The unit production cost was reduced by 2.3 NT dollars/ton considering the reduction of fuel cost and air pollution fee（the cost reduced about 0.12%）. For RAP dried by natural gas, the removal efficiencies of volatile organic carbons (VOCs) and odor in the flue gas treated by an integration of cyclone and incinerator were 53.8% and 92.4%, respectively. Consequently, odor was not contributed all by VOCs as was justified by unequal removal efficiencies. The removal efficiency of Polycyclic Aromatic Hydrocarbons (PAHs) was only 18.67% when RAP was dried by using No.6 heavy oil and flue gas treated by an integration of cyclone and incinerator. The discharged concentration of PAHs from outlet was greater than that from inlet. This was due to the use of No.6 heavy oil to cause an increase of PAHs content. There are two plants with similar manufacturing process and using the same fuel for drying in this study, however, the deviations of emission factors varied from -6.8% to 60.6%. Therefore, pollution amounts of a plant estimated by using emission factor of other plant may cause a big error.
For the pollutants dispersion modeling by using Industrial Source Complex (ISC) at the three selected receptor sites, the combined pollutant increments and background concentrations for TSP, PM10, PM2.5, SOx, and NOx were 43.37-44.13 μg/m3, 36.88-36.99 μg/m3, 18.50-18.50 μg/m3, 6.3~6.74 ppb, 26.96-27.88 ppb, respectively. All modeled pollutant concentrations do not exceed National Ambient Air Quality Standards. The maximum ground concentrations of TSP, SOx, and NOx are 120 m, 1161 m, and 1161 m, respectively, counted from the main gate of plant A.
By injecting odor emission standard level of 2000 into the discharging stack of plant A, the simulated odor values of various stories at the three selected receptor sites were in the ranges of 1.65~12.67, 2.04~19.79, 1.84~16.18, respectively. The residents could smell the odor at the elevations of 20, 16, 18 stories at the three sites. It indicates that resident complaints could occur even when the flue gas of a plant is in compliance with the odor emission standard. The maximum odor level was modeled at 63 m from the main gate of plant A with an elevation of 75 m (around 25-story high). Finally, this study is concerned with the health risk of Benzo(a)Pyrine (BaP) in the glue gas of natural gas combustion of HMA. The whole-life cancer risk of residents at the three selected receptor sites were estimated to be 2.08×10-5, 8.91×10-6, and 3.96×10-6, respectively. The values are considered to be in the acceptable risk levels. |
