Ammonia release characteristics during desulfurization wastewater evaporation: Mechanisms and implications

Abstract

This study investigated the mechanisms of ammonia release during desulfurization wastewater evaporation and its potential environmental impacts. A single droplet evaporation device (SDD) assessed the wastewater evaporation and ammonia release characteristics. Approximately 8.5 % of ammonia was released during the free water evaporation period (0–35 s). As the droplet underwent shell inflation-deflation and core-shell drying, the remaining ammonia was mainly released due to increased vapor pressure and poor thermal stability of ammonium salts. The wastewater properties, especially pH value, greatly influenced the release of ammonia. Alkaline wastewater exhibited a significantly higher ammonia release rate. Ammonia migration and transformation were studied in a 600 MW power plant. Approximately 9.2–11.7 % of ammonia was released, while the rest was retained in solid form within the evaporation product. Characterization techniques and DFT simulations showed that the released NH3 probably combines with fly ash due to the water vapor, HCl, SO3, and other acidic gases in the flue gas. Risk analysis suggested that ammonia release during evaporation would not significantly increase ammonia concentration in flue gas or hinder fly ash comprehensive utilization. However, when handling desulfurization wastewater with high-concentration ammonia, it was essential to consider the potential corrosion of downstream equipment caused by released ammonia.