| Popis: |
The pyrolysis reaction, which is an important source of PAH formation near the grate bed region of a waste incinerator, is the first step for a combustion process from the viewpoints of formation of the hazardous air pollutants (HAPs) in the flue gas. Polystyrene (PS) pyrolyses with calcium oxide catalyst under an inert (100% nitrogen) and an oxidative (10% oxygen+90% nitrogen) atmosphere at 600, 700 and 800°C were performed in a laboratory quartz reactor. The 16 priority polyaromatic hydrocarbons (PAHs) in the pyrolysis products were analyzed with a high-performance liquid chromatograph (HPLC) equipped with a wavelength-scanning ultraviolet (UV) detector. At 600°C, calcium oxide was observed to promote PAH formation; while at 800°C, it reduced PAH formation. Such observed results are explained by the mechanisms involving the reaction of the gaseous hydrocarbon PAH precursors with both free electrons and hydroxyl free radicals. In addition, as pyrolysis temperature increased, both the species number and quantity of the priority PAHs increased. A sharp increase in PAHs was observed at 800°C under oxidative condition, as well as at 700 and 800°C under inert condition. Thus, it is suggested that the monitoring and control of pyrolysis parameters, which are always neglected during the design or operation of a commercialized incinerator, can provide some important information on the control of PAH formation from waste incineration because pyrolysis occurs during the earlier stage of an incineration process. |
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