10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Observations of Sulfate Aerosol Condensation in Flue Plumes from Coal-Fired Power Plants Equipped with WFGD
JIANMIN CHEN, Xiang Ding, Di Wu, Xianmang Xu, Qing Li, Fudan University
Abstract Number: 233 Working Group: Aerosol Chemistry
Abstract More than half of the annual worldwide coal consumption is consumed in China, where about a half is used for electricity generation. Coal combustion is acknowledged to be one of the largest contributor to China’s haze pollution. Therefore, a new regulation for controlling air pollutant emissions from coal-fired power plants (CFPPs) has been executed in 2014. This policy has been called the standard of “Ultra Low Emission”. To meet the standard, all CFPPs are required to install flue gas desulphurization (FGD) and denitration systems. More than 90% of FGDs use the wet process of limestone-gypsum FGD technology, which is also the world’s most widely used FGD technology to remove SO2 and particulate matters (PMs). However, there is always a long “White Plume” emitted from industrial stacks, if it installed a wet FGD. The “White Plumes” have being attracted great public interest due to their possible negative effects on climate and health risks.
This study firstly reports characteristics of PMs in the “White Plumes” based on measurement at three CFPPs equipped with limestone-gypsum or seawater FGDs. Mass concentrations of water soluble ions (WSIs) in PM samples collected at wet FGD outlets were about 70-90% higher than that collected at the FGD inlets. Highest values were observed for PMs collected in the “White Plumes”. The relative percentage of sulfate ions (SO42-) in total WSIs were about 27%, 54%, and 64% in the three locations, respectively, while relative percentage for ammonia ions (NH4+) were about 11%, 16% and 16%, respectively. Droplets collected in the “White Plumes” showed acidity with a pH in the range of 2 ~ 4 and high WSI concentrations of about 3 ppb. The relative percentage of SO42- and NH4+ in total WSIs were about 63% and 18%, respectively. The increased values of SO42- and NH4+ in plumes are probably due to the condensation of SO2/SO3 and NH3 (slipped from denitration systems), since the temperature of flue gas in stacks (about 25 oC and 50 oC for seawater and limestone-gypsum FGDs, respectively) is generally higher than that of ambient air.
These condensable species, including H2O, SO2/SO3, NH3, and VOCs, can condense on existing PMs via heterogeneous nucleation. The results indicate that reported results in previous publications (obtained in stacks) commonly under-estimate the primary PMs emitted from CFPPs equipped with wet FGDs, especially SO42- and NH4+ concentrations. These experimental findings improve the basic understanding of potential climate and health effects of the “White Plumes”.