[PCDD/F formation and its mass balance in a MSW incineration system]

PCDD/F distributions in a two-stage reciprocating grate municipal solid waste (MSW) incinerator under two kinds of operating conditions were investigated by sampling the ashes, flue gases and bottom ashes at different positions, and the mass balance was calculated. At the boiler outlet, the concentration of PCDD/F in the flue gas is 2.602 ng x m(-3) and 1.236 ng x m(-3) under operating condition 1 (RUNI) and operating condition 2 (RUN2), respectively. A significant formation of PCDD/F was found in the sections of semi-dry scrubber (SDS) and cyclone precipitator (CP), in which the temperature of flue gas was in the range of 260-180 degrees C. Compared with PCDD/F level measured at the boiler outlet, the total concentration of tetra-to octa-CDD/F measured at the CP outlet increased 82.2% and 17.6% under RUN1 and RUN2, respectively. At the bag filter (BF) section, about 90% of PCDD/F was removed from the flue gas by the precipitation of fly ash. The PCDD/F homologue patterns were almost similar for the boiler ash, CP ash, BF ash and the flue gases. The higher O2 content in flue gas led to a larger PCDD/F yield, but the variation of O2 level did not give rise to a systematical change of PCDD/F homologue pattern. Under RUN1, 10.4%, 3.2%, 9.3%, 64.1% and 13.0% of formed tetra-to octa-CDD/F were distributed into bottom ash, boiler ash, CP ash, BF ash and emission gas, respectively. The corresponding values were 8.6%, 8.0%, 9.4%, 66.7% and 7.3% for RUN2, respectively.