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Abstract In an electrostatic precipitator, particles migrate to the collecting plates through electrostatic force. Simultaneously, the effect of gravity and hydrodynamic drag force will cause these particles to vacate the plates. Emission concentration and removal efficiency gradually stabilize after the particles pass through multiple electric fields, and this stability value determines the high limit of electrostatic precipitation capacity. In this study, the balance between particle electrostatic trapping and air re-entrainment was investigated through a closed-loop electrostatic precipitator system, and the behavior of the particles deposited into the collecting plates was qualitatively analyzed. The particle emission concentration was reduced significantly when residence time was within 40 s. The particle concentration reached its limit and remained relatively stable after remaining stable for 100 s in the electric field. The applied voltage, velocity of flow, and temperature are the influencing factors considered in this study, here it was found that the decreased flow velocity, temperature and rising voltage were benefiting to particles removal efficiency. The ultimate emission concentration gradually decreased from 13.14 mg/m3 to 7.19 mg/m3 while the velocity of the flow decreased from 0.376 m/s to 0.240 m/s at the temperature of 700 K. The ultimate emission concentration gradually increased from 6.24 mg/m3 to 1.79 mg/m3 while the temperature decreased from 800 K to 400 K when the flue gas velocity was 0.376 m/s, and the applied voltage was at its maximum which can be used at the corresponding temperature. The ultimate emission concentration gradually decreased from 19.5 mg/m3 to 6.0 mg/m3 when the flue gas temperature was 400 K, and the velocity of the flow was 0.376 m/s, with the increase in voltage from 14.9 kV to 32.5 kV. In addition, particles of different size segments and specific resistances exhibited various characteristics in this study because the electrostatic and van der Waals forces were significantly affected by the particle size. Graphic abstract Unlabelled Image Highlights • The balance between particle collection and re-entrainment was studied. • A closed-loop electrostatic precipitator system was designed. • The ultimate collection efficiency were proposed. [ABSTRACT FROM AUTHOR]

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 Electrostatic precipitators (ESPs) are considered as cost-effective technology for separating the charged particle from flue gas. In this paper, a modified ESP model was developed to investigate the effects of charged particle on the electric field, ion density, particle charging and migration regarding various particle concentrations. Coupled processes of corona discharge, flow field, particle charging and transport were considered. Results showed that the particle space charge presented trajectory-dependent effects on the distributions of electric field and ion density in the gas flow direction. With the particle concentration increasing from 0 to 200 mg/m3, the electric field strength on the electrode surface was inhibited from 1.32 × 106 to 1.24 × 106 V/m, while the electric field strength on the plate surface was raised from 7.1 × 105 to 8.3 × 105 V/m. By contrast, the ion density within the whole domain decreased when particle space charge considered, and it decreased by more than 40% when the particle concentration was 50 mg/m3. The particle charging rate decreased due to particle space charge effects and consequently the overall particle charge decreased by 45.7% as particle concentration increased to 200 mg/m3. The correlation between collection efficiency and corona current was discussed, and it showed that the two didn't vary synchronously with the increasing concentration. A criterion for efficiency deterioration, under corona suppression conditions, was first proposed for instructing ESP design and operation. Graphical abstracts Unlabelled Image Highlights • A modified ESP model was established to study the particle space charge effects. • Corona discharge, flow field, particle charging and transport were coupled. • Correlation between corona current and collection efficiency was analyzed. • A criterion for ESP performance deterioration was first proposed. [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]

The corona discharge characteristics of an electrostatic precipitator are an important factor that affects particle charging and collection. The electrical characteristics of a wire-plate electrostatic precipitator and the particle transport behavior were studied by considering the electrohydrodynamics (EHD) and the effect of particle space charge through numerical simulation. Simulation results showed that the effect of particle space charge intensifies in extremely small particles, such as submicron particles. This condition significantly influences electric field, ionic charge density, and current. The electric field intensity and ionic charge concentration significantly decreased. The reduction in the minimum field intensity between the electrodes decreased to 50%, and the lowest concentration of the ionic charge tended to 0 when the particle size varied from 5 µm to 0.1 µm. When the applied voltage increased from 13 kV to 40 kV, the space charge ratio of the particles larger than 2 µm was reduced to almost 0 but remained at a high level for the particles less than 0.5 µm whose corresponding current was lower by 20% than that without particle condition. The ionic wind in the electrostatic field also weakened because the movement of ions was restricted for corona suppression, leading to decreased corona current. Furthermore, the particle transport behavior was compared considering the effect of particle space charge. Results indicated that the difference between the two conditions increased from 1.3% to 47.4% with decreasing particle size from 5 µm to 0.07 µm. In addition, the particle migration velocity of the 0.1 µm particles increased by 9.8%, from 0.2 to 0.1 µm, even if the drag force was reduced when considering the particle space charge. A modified I–V equation was provided, with fitting coefficient of 0.996, and is thus worthy of reference in practical application. [ABSTRACT FROM AUTHOR]