| dc.description.abstract | 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. | en_US |