Asphalt plants and associated equipment including storage silos, tanks, aggregate handling equipment and related processes emit air contaminants including oxides of nitrogen, carbon monoxide, volatile organic compounds, oxides of sulfur, particulate matter and toxic air contaminants. This equipment requires a permit to operate.
Hot mix asphalt plants typically include storage hoppers, silos and material conveyance equipment for aggregate and liquid asphalt used to make the asphaltic concrete. The main plant consists of separate or a combined dryer and mixing drum/barrel including a large burner (typically natural gas or propane fired). The mixture is transferred to storage silos loaded into trucks for transport to paving projects. The plants typically require a hot oil heater to maintain the liquid asphalt at correct temperature/viscosity. Plants may also include mixing and blending tanks for producing rubberized asphalt or other specialty asphalt products. Emissions are controlled through a variety of means, typically including water to minimize dust during aggregate transfer, condensers to prevent vapor emissions from liquid storage tanks, controlled combustion/low-NOx burners to minimize combustion emissions, a baghouse to remove particulate from the dryer/drum exhaust and a blue smoke control filter to collect vapor, smoke and odor emissions during transfer, storage and load-out to transport trucks.