Formation and fate of PAH during the pyrolysis and fuel-rich combustion ofcoal primary tar

The formation and fate of polycyclic aromatic hydrocarbons (PAH) during the pyrolysis and fuel-rich combustion of primary tar generated under rapid he ating conditions have been studied. Experiments were performed using a quar tz two-stage reactor consisting of a fluidized-bed reactor coupled to a tub ular-flow reactor. Primary tar was produced in the fluidized-bed reactor by rapid coal pyrolysis at 600 degrees C. The freshly generated tar was subse quently reacted in the tubular-flow reactor at 1000 degrees C under varying oxygen concentrations covering the range from pyrolysis to stoichiometric oxidation. PAH species present in the tars recovered from the tubular-dow r eactor were analyzed by highperformance liquid chromatography (HPLC). Twent y-seven PAH species, varying from 2-ring to 9-ring structures, were identif ied, including benzenoid PAH, fluoranthene benzologues and indene benzologu es. The majority of PAH species identified from pyrolysis were also identif ied in the samples collected from oxidation experiments. However, three pro ducts, 9-fluorenone, cyclopenta[def]phenanthrene and indeno[1,2,3-cd]fluora nthene, were produced only during oxidizing conditions. The addition of a s mall amount of oxygen brought about measurable increases in the yields of t he indene benzologues and g-fluorenone, but the yields of all PAH products decreased at high oxygen concentrations, in accordance with their destructi on by oxidation. Possible formation and destruction mechanisms of PAH under fuel-rich conditions have been discussed. (C) 2000 Elsevier Science Ltd. A ll rights reserved.