Release and migration characteristics of chlorine during the desulfurization wastewater evaporation process

The spray evaporation technology was a practical approach to realize zero liquid discharge (ZLD). In the evaporation process, the chlorine in desulfurization wastewater would precipitate out and exist in the flue gas, causing a significant impact on the desulfurization system. In this work, the release and migration characteristics of chlorine during the evaporation process were first studied in the lab and pilot-scale platform. The thermal stability of three common chlorine salts was evaluated, and the result indicated that the magnesium salt showed the worst thermal stability, which tended to release chlorine by the effect of hydrolysis. The influences of flue gas temperature, pH value, Cl- concentration of desulfurization wastewater, and gas to liquid ratio were investigated. The results showed that the higher flue gas temperature was conducive to the enrichment of chlorine in the bottom ash; When the pH value of wastewater was adjusted to 9, about 49.8% of gaseous chlorine release could be reduced; Besides, the release of chlorine was also affected by the Cl- concentration of wastewater. In addition, the high gas to liquid ratio led to the higher chlorine release level due to the lift of temperature distribution in the drying tower.