Reduction of PCDD/F Formation in MSWI by a Process-Integrated SO 2 Cycle

PCDD/F formation in MSWI predominantly takes place by de novo synthesis in the ash deposits in the boiler. Permanently high SO₂ concentrations cause sulfation of the boiler ash and the fly ash, which leads to low chloride concentrations in the ash deposits. This results in very low PCDD/F formation rates. High SO₂ levels can be established in an efficient way by a process-integrated SO₂ cycle, with only the SO₂ generated by the combustion process being used. The S-recycling process can be supported by reducing the transfer rates of CaO particles to the flue gas by a low primary air supply. No additional source of sulfur is needed. No negative effects of the S-recycling process on the separation of other pollutants like Hg could be observed. These findings indicate that the PCDD/F emission standards can already be met upstream of the flue gas cleaning system by these primary measures only. The flue gas cleaning efforts can be reduced without changing the emission standards.