Modeling of Polycyclic Aromatic Hydrocarbons stack emissions from a hot mix asphalt plant for gate-to-gate Life Cycle Inventory

Only few LCI data are by now available concerning Polycyclic Aromatic Hydrocarbons emitted by asphalt plants. Depending on the type of airborne emissions the influence of plant technology and of input materials can be significant on environmental performances of products. Then, the use of generic Life Cycle Inventory (LCI) data is not satisfying because results do not allow the comparison between technologies, and it is necessary to produce data for gate-to-gate technologies. The objective of this paper is to provide suitable LCI data for PAH airborne stack emissions of an asphalt plant equipped with a parallel drum mixer and fed with natural gas. The purpose is not to serve as a generic LCI data, but on the contrary, to serve as a first step to future comparisons to other asphalt manufacturing technologies (batch mix, counter flow drums) and to other fuels (fuel oil). The studied (and sampled) PAH are chosen from the US-EPA list of carcinogens, or expected carcinogens. Operation conditions were varied (different asphalt manufacturing temperatures and production rates) in order to obtain inventory data more representative from various working conditions. PAH values are found highly variable, probably depending on instability of natural combustion chemical reactions. An empirical model is proposed that defines a multi-linear relationship between some PAHs emissions and both the bitumen content in asphalt and the CO/CO2 ratio. The model is discussed in terms of physic-chemical significance, limits of application and feasibility for LCA.