[Effect of a Wet Flue Gas Desulphurization System on the Emission of PM_2.5 from Coal-Fired Power Plants]

Wet flue gas desulphurization (WFGD) is wildly used to control SO₂ emission from coal-fired power plants. The influence of WFGD on particulate matter (PM) emission has recently drawn significant public attentions in China. In this study, PM_2.5 was collected at both the inlet and outlet from three WFGD units, including a single scrubber lime-stone-gypsum FGD unit, a cascade scrubber lime-stone-gypsum FGD unit, and a seawater FGD unit. PM_2.5 mass concentrations and their chemical compositions were analyzed. A method to calculate the addition and removal ratios is proposed according to the concertation of PM_2.5 components, such as Ti, Pb, Cr, and V. The results indicate that the removal ratio was similar between the three WFGD units (77.1% on average). However, the addition ratio varied significantly. The performance of the cascade scrubber lime-stone-gypsum FGD unit was best, with a lower addition ratio of 8.6%, which is attributed to the weaker evaporation of desulphurization slurry droplets in their second tower under the low temperature of the flue gas. The addition ratio of the seawater FGD unit was also low (23.9%) because of its low concentration of solids in the seawater. The addition ratio of the single scrubber lime-stone-gypsum FGD system was highest, with a value of 162.3%, which was probably due to the low efficiency of the de-mister.