Effects of Wet Flue Gas Desulfurization and Wet Electrostatic Precipitator on Particulate Matter and Sulfur Oxide Emission in Coal-Fired Power Plants

Wet flue gas desulfurization (WFGD) and wet electrostatic precipitator (WESP) are widely used in coal-fired power plants (CFPPs) for pollutants control. In this work, the emission characteristics of PM10 (particulate matter (PM) with aerodynamic diameter less than 10 mu m, similarly for PM1 and PM2.5) and sulfur oxides (SO3 mainly SO2 and SO3) and the water-soluble ions in particles were investigated for WFGD and WESP in two CFPPs. One of the CFPPs was equipped with one absorption tower for the desulfurization process (one-stage WFGD, named as plant A), and the other one was equipped with two absorption towers in series (two-stage WFGD, named as plant B). SO3 removal efficiencies were 27.3% in one-stage WFGD and 81.6% in two-stage WFGD. The removal efficiencies of WFGD and WESP on PM10 were 64.0-70.3 and 57.5-79.2%, respectively. WFGD had a great effect on particle size distributions (PSDs). The concentrations of particles with diameters of 0.021-0.365 and 0.021-1.620 mu m showed a significant increase after one-stage and two-stage WFGD, respectively. In plant A, the removal efficiencies of WESP on PM with diameters of 0.02-2.5 mu m were 68.8-74.3%, and the efficiencies decreased to 57.2-58.5% when the diameter was larger than 2.5 mu m; moreover, the peak of PSDs shifted from 2 to 4.0 pm after WESP; while the removal efficiency increased with the particle size in plant B. The water-soluble ion concentrations of SO42-, Cl- and Mg2+ in PM10 increased dramatically after the desulfurization process, but all the detected ions were reduced by 50% in WESP. The stoichiometric analysis on the balance of anion and cation was studied. The values of cation equivalent/anion equivalent was less than 1 before WFGD and larger than 1 after WFGD and WESP. The emission factors of PM1, PM10, SO2, and SO3 at the final emission were in the range of 5.3-15.4, 7.6-20.1, 15.9-21.7, 105.3-179.6, and 30.1-49.4 g.t(-1) respectively.