Pilot-scale study of desulfurization wastewater evaporation: Emission and migration characteristics of mercury

The hot flue gas evaporation technology exhibited a significant advantage in desulfurization wastewater zero discharge. However, the mercury emission during the wastewater evaporation process was a potential risk that may limit the popularization and application of this technology. The emission and migration characteristics of mercury were studied on the lab-scale furnace and pilot-scale wastewater evaporation system, respectively. The Hg in the wastewater would undergo the release-oxidation/adsorption process. Approximately 93.6% of Hg existing in the wastewater would firstly release due to the high volatility and component of SO32- and Cl-. Then, the released Hg would be further affected by the oxidation and adsorption mechanism. The generated HCl gas atmosphere and the active substances in the solid content would oxidize most of the released Hg0 and lift the Hg2+ proportion in the flue gas. Besides, the adsorption effect enhanced the conversion from the gaseous Hg to the Hgp, causing a high Hg proportion of 89.4% in the final solid evaporation product. The findings in risk assessment demonstrated that the hot flue gas evaporation technology would not upset the Hg distribution or cause extra Hg emissions for the whole power plant. However, the large water/acid-soluble fraction of Hg in the evaporation product should be considered in the storage and disposal procedure.

Automated summary

The hot flue gas evaporation technology has significant advantages in zero discharge of desulfurization wastewater, but mercury emissions are a potential limitation. Research has shown that mercury in the wastewater undergoes a release-oxidation/adsorption process. Most of the released mercury is affected by oxidation and adsorption mechanisms, resulting in a high mercury content in the final solid evaporation product. Risk assessment results indicate that this technology does not disrupt mercury distribution or cause additional mercury emissions for the entire power plant, but the large water/acid-soluble fraction of mercury in the evaporation product should be considered in storage and disposal.