摘要
The most abundant and typical reducing agent for oxidized mercury in the slurry of wet flue-gas desulphurization(FGD)is the absorbed sulphur dioxide(SO_(2)),which is present as different species of bisulphite or sulphite,depending on the pH of the slurry.In this study,two different measurement principles for continuous sulphite measurement in the slurry of lab-scale FGD were investigated to check their feasibility to be implemented in a wet FGD.The first method is based on light absorbance at the characteristic wavelength of sulphite measurement using a spectrophotometer and,in the second method,sulphite is measured as sulphur dioxide using a gas sensor.In addition,the correlation of sulphite concentration and mercury(Hg)in the slurry can be shown by measuring sulphite semi-continuously.It was concluded that using a spectrophotometer leads to distorted results.In contrast,measuring sulphite as SO2 in the gas phase proved to be more selective.The implementation of the measurement technique in the lab-scale FGD showed promising results for sulphite measurement.Thus,the correlation of Hg and sulphite concentration could be shown at different synthetic slurries containing different halides.Using a slurry without halides demonstrated the ambivalent influence of sulphite in reactions involving Hg,in which sulphite acts as a ligand for Hg complexes as well as a reducing agent,depending on the existing concentration.However,in the presence of halides,the role of sulphite was less significant.
