Release characteristics of chloride during single droplet drying process of desulfurization wastewater

Abstract

BACKGROUND:The release characteristics of chloride during the evaporation process of desulfurization wastewater droplets were studied by single droplet drying experiments. The mass, size and temperature variation of droplets during the evaporation process were measured and the release mechanism of chloride was revealed. In addition, the influence of temperature, pH value and metal cation species on the release characteristics of chloride was explored.RESULTS: Combined with the evaporation process, chloride release could be divided into three stages: free water evaporation, shell instability and crystallization chloride salt hydrolysis. In the initial stage, moisture removal was the dominant phenomenon and almost no chloride release was observed. During the stage of shell instability, cycles of droplet inflation and rupture took place, and the release amount of chloride accounted for 51.2% of the total release amount in the typical working conditions. Hydrolysis of crystallization chloride salt played a key role in chloride release and about 46.0% chloride release could be traced during the last stage. High temperature would boost the chloride release; with pH value increasing from 3 to 9, chloride release decreased from 39.7% to 28.8%; a higher magnesium concentration would enhance the chloride release due to the greater hydrolysis strength. CONCLUSION: Chloride in the wastewater droplet would not transfer to the gas phase until the evaporation proceeded to the stage of shell instability. The chloride release characteristics investigated in this work are expected to control the HCl emission in practical engineering of hot flue gas evaporation.