Field Measurements on the Emission and Removal of PM2.5 from Coal-Fired Power Stations: 4. PM Removal Performance of Wet Electrostatic Precipitators

This study reports the impacts of two commercial wet electrostatic precipitators (WESPs) on the emission of fine particulate matter (PM 2.5 ) and SO 3 . Field measurements were carried out at two 300 MW coal-fired power station units equipped with WESPs between limestone-gypsum wet flue gas desulfurization (WFGD) unit and the stack. PM samples were collected at the inlet and outlet of the WESPs as well as the inlet and outlet of the dry ESP, and SO 3 was collected at the inlet and outlet of the WESP. The results show that 99.21% of the PM 2.5 emitted from the boiler is removed in the dry ESP. The WFGD has a removal efficiency of 24.19% for PM 2.5 but produces new gypsum particles and then increases the emission of PM 1 (by ∼24%). PM at the WESP inlet is centered at 1 μm, and after passing through the WESP, concentrations of PM 0.3, PM 1, and PM 2.5 are reduced by 73.72–93.75%, 83.33–94.41%, and 79.91–90.23%, respectively. SO 3 emission is also reduced by the WESP due to the capture of H 2 SO 4 via electrostatic force and the absorption of SO 3 by the basic sprayed liquid, with a removal efficiency of 52.03–59.09%. However, new PM larger than 2 μm is generated from the entrainment of circulating liquid droplets in the WESP, which partially offsets the capture of PM 2.5 . As the boiler load decreases from 100% to 70%, the removal efficiency of PM 0.3 increases a little, whereas the removal efficiencies of PM 1 and PM 2.5 decrease from 89.34% and 89.85% to 83.33% and 79.71% due to the decreased removal efficiency for PM larger than 2 μm. WESP contributes less to the PM 2.5 removal compared to the dry ESP (0.54% vs 99.27%) while it effectively reduces fine PM emission.