Condensable particulate matter emissions regulated by flue gas desulfurization technologies in typical industrial plants

Abstract

Condensable particulate matter (CPM) emissions have exceeded filterable particulate matter from industrial plants under strict emission standards. However, how CPM emission characteristics are affected by air pollution control devices (especially end-of-pipe flue gas desulfurization (FGD) systems) remains to be investigated. Here, we systematically demonstrated CPM emissions regulated by various FGD systems through field measurements of 22 typical industrial sites. Inorganic CPM (57.6 ∼ 99.5 % of CPM) predominantly consisted of water-soluble ions, whose concentrations were distinct between the inlet and outlet of FGD units. SO₄^2- or Cl^- mainly contributed to inorganic CPM before desulfurization, while SO₄^2- and NH₄⁺ accounted for 49.2 ∼ 96.3 % of inorganic CPM after FGD. Higher removal efficiencies for Cl^- (98.1 ± 1.9 %) than SO₄^2- (50.1 ± 23.8 %) in partial lime-gypsum-wet FGD systems could convert Cl^--rich CPM into SO₄^2--rich CPM. Ammonia-wet FGD and activated coke FGD failed to address NH₃ slip issues effectively, leading to NH₄⁺- rich (44.0 ∼ 96.0 %) CPM after desulfurization. Conversions of precursors (i.e., NH₃, HCl, and SO₃) before and after FGD were consistent with those of water-soluble ions. This study revealed chemical-specific transformations of CPM under different FGD processes, highlighting the control of the NH₃ slip to reduce CPM emissions.