Study on the ammonia emission characteristics in an ammonia-based WFGD system

Ammonia and its contribution to secondary organic and inorganic aerosols are harmful to the environment and human health. The ammonia-based wet flue gas desulfurization (ammonia-WFGD) is effective in removing SO2 from industrial flue gas but also is a potential source of ammonia emission. In this paper, experiments were done in a pilot-scale ammonia-WFGD system. The definition of the ammonia emission was first stated to include the gaseous ammonia, and the solid or liquid aerosols containing ammonia. The emitted ammonia was then distinguished into the filterable ammonia, the condensable ammonia, and the gaseous ammonia based on their behaviors during emission processes. A piecewise sampling system was built accordingly to sample them, respectively. The parameters, such as the flue gas temperature, the desulfurizing solution temperature, the solution concentration, and the pH, were adjusted to investigate their influences on the ammonia emission characteristics. Results showed that large amounts of ammonia were emitted from the ammonia-WFGD system, in which the gaseous ammonia accounted for around 19%, with the filterable ammonia and the condensable ammonia sharing the rest 81%. The flue gas temperature, the solution concentration, and the solution pH were equally important to the total ammonia emission control. Theoretically, optimizing any one of the above three parameters could lower the ammonia emission by 38%. All the parameters had impacts on the individual ammonia emissions, although to different extents. It is worthwhile to conduct further researches on parameter optimizations to achieve better ammonia emission control.