The Effects of Fluoride Complexes in Wet Limestone Flue Gas Desulfurization.

Abstract

In the wet limestone flue gas desulfurization process (FGD), aluminum/fluoride complexes (AIFx) are sometimes formed in liquid phase and inhibit the dissolution of the limestone, thereby reducing the desutfurization performance.To clarify the mechanism of this phenomenon, bench-scale tests simulating the operating conditions of the FGD were conducted.The results obtained indicate that the formation of AIFx depends on such factors as fly ash loading and aluminum content in limestone. Earlier papers have not discussed the latter factor sufficiently. The authors also observed that magnesium/fluoride complex (MgF+) potentially inhibits the dissolution of limestone. As a countermeasure to AIFx, it was demonstrated that the addition of strong alkali during operation can decompose AIFx and prevent inhibition of limestone dissolution.The decomposition of AIFx was directly detected by 19F FT-NMR.Equilibrium model calculations theoretically support the decomposition of AIFx by a strong alkali added to an absorbent with pH kept within an appropriate range.