Mechanism of SO3/H2SO4 transformation and reduction in wet flue gas desulfurization systems

•H2SO4 vapor and aerosols coexist at the inlet of wet flue gas desulfurization (WFGD).•Most, but not all, H2SO4 vapor is transformed into aerosols in the scrubber.•A small fraction of gaseous H2SO4 remains in flue gas at the WFGD scrubber outlet.•The demister in the scrubber is more efficient at reducing H2SO4 than the droplets. In this study, a unique sampling unit combining quartz wool filtration and salt adsorption, which can measure aerosol and gaseous H2SO4 simultaneously, was adopted to reveal the transformation and reduction of SO3/H2SO4 in a lab-scale wet flue gas desulfurization (WFGD) scrubber. The results showed that H2SO4 in flue gas at the inlet of the WFGD scrubber is in both gaseous and aerosol states, and the gaseous state constitutes a larger proportion, differing from the conventional realization that all H2SO4 at WFGD scrubber inlets is gaseous. The experiments showed that the amount of H2SO4 aerosols increased, and that of H2SO4 vapor decreased in the scrubber, indicating H2SO4 transformation from a gaseous to an aerosol state after quenching. However, there is always a small portion of H2SO4 vapor that could be detected at the outlet, suggesting that H2SO4 cannot be completely converted to aerosols in the scrubber, differing from traditional assumption. We also found that spraying droplets could reduce H2SO4 but with low efficiency. The demister installed at the scrubber outlet is more efficient at reducing H2SO4 than the droplets, which inspires a new understanding of the mechanism of H2SO4 reduction in WFGD processes.