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Highlights • SO 3 formation and phase transformation mechanism in coal-fired plants are studied. • The adverse effects of SO 3 on the utility operations and environment are analyzed. • Different SO 3 test standards and measurement methods are compared. • Various SO 3 control technologies are reviewed and compared. • Future trends of SO 3 emission limits and control strategies are prospected. Abstract The formation and emission of sulfur trioxide (SO 3) in coal-fired power plants has received increasing attention due to its adverse effects on the operation of plant and environment. With the wide application of selective catalytic reduction (SCR) systems, the problem caused by SO 3 has become severe, especially when high sulfur coal is burned. Emission regulations of SO 3 for coal-fired power plants, which promote the development of SO 3 measurement and control technologies, have been set in some countries and regions. In this paper, recent advances in the formation, transformation, measurement, and control mechanism and technologies of SO 3 in coal-fired power plants were summarized. The formation mechanisms of SO 3 in boiler and SCR systems and its form transition and corresponding effects on the performance of power plants were analyzed. Different SO 3 test standards and methods were compared, and online SO 3 monitor based on isopropanol absorption method were developed. Various SO 3 control technologies, including simultaneous and specific removal technology, were summarized. Low-low temperature and wet electrostatic precipitators could remove up to 90% SO 3 /H 2 SO 4 aerosol, and the removal efficiency of SO 3 in wet flue gas desulfurization can be enhanced to 80% by absorber optimization and inlet flue gas temperature decrease. For power plants that burn high-sulfur coal, the injection of alkaline sorbent before the SCR or air preheater system can remove more than 90% of SO 3 to decrease the formation of NH 4 HSO 4 and the pressure drop in the air preheater. High SO 3 removal technology and strategies for different scenarios were proposed to meet different SO 3 emission requirements in the future. [ABSTRACT FROM AUTHOR]

Abstract Improving the removal efficiency of fine particle is significant for the elimination of particle emission from coal-fired power plants. This work reports a combined wet electrostatic precipitator (WESP) enhanced by a novel perforated pre-charger to efficiently remove fine particle from wet flue gas. Penetration and charging characteristics of fine particle through the WESP were evaluated as a function of particle size. The collection performance was investigated under controlled gas temperatures and varied electrical conditions. Results showed that there was a maximum penetration ratio around 0.1 μm and it decreased with the increasing applied voltage. A portion of the escaping fine particles were not charged through the WESP, and the size limit for partial charging can be reduced to 0.025 μm when the applied voltage increased to 32 kV. Reducing gas temperature leaded to an obvious improvement in collection efficiency for particles in the size range of 0.1–1.0 μm. The test results of different electrodes showed that both the corona current and maximum collection efficiency ranked in the order of pin > sawtooth > rod. With the assistance of pre-charger, the particle charging was significantly improved and the charge amount was more than doubled. Consequently, the effective migration velocity for PM 0.1 , PM 1.0 and PM 2.5 increased by 69.9%, 65.7% and 34.2%, respectively. Actual application results showed that the average PM emission level can be reduced to 0.43 mg/m3 by the combined WESP in a 1000 MW coal-fired power plant. Graphical abstract Unlabelled Image Highlights • A combined WESP was developed to help to realize ultra-low emission. • Particle penetration and charging were evaluated as a function of particle size. • The charge amount was more than doubled assisted with the pre-charger. • The average PM emission level can be reduced to 0.43 mg/m3 in an actual plant. [ABSTRACT FROM AUTHOR]