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Aiming at enhanced particulate matter (PM) removal of electrostatic precipitators (ESPs) in coal-fired power plants, a pulse energization power supply that generates high-voltage pulses superimposed on a high-voltage dc was designed. The integrated theories of corona discharge, particle charging, and removal were presented, and the pulse energization strategy was studied through fractional particle removal simulation. The conclusion of simulation stated that pulse energization could significantly improve particle charge with a maximum enhancement at a particle diameter of $20~\mu \text{m}$ , while the fractional particle removal efficiency shows a different distribution that removal of particles less than $2.5~\mu \text{m}$ had the most significant enhancement. Based on the design and simulations, a full-scale comparative operation study testified the potential of dc + pulse energization to enhance particle removal with a limited power consumption increase. Pulse energization was applied to different industrial ESPs with various design and operation parameters and shown multicondition adaptability in PM removal enhancement, with the emission reduction ranging from 45.48% to 58.00% and outlet concentration from 8.60 to 47.48 mg/Nm3, proving it a convenient and economical method in the performance boost of industrial ESPs. [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]

This study investigated the influence of electrode configuration on corona discharge and particle collection from 300 K to 900 K. Electrodes of different shapes (rod, saw, and screw), diameters (3, 5, and 8 mm), and intervals (55, 110, and 165 mm) were tested in an experimental-scale electrostatic precipitator (ESP). Results showed that a high current was generated with a saw electrode and increased the particle collection efficiency, particularly for fine particles (diameter smaller than 0.1 μm), with the best particle collection efficiency being 99.8% at 300 K. However, with an increase in temperature, the rod electrode obtained an applied voltage higher than those of other electrode types and, as a result, generated relatively high particle collection efficiencies at 700 K and 900 K. Increasing the electrode diameter from 3 mm to 5 mm improved the applied voltage, whereas increasing this diameter from 5 mm to 8 mm reduced the discharge current. Among electrodes with different diameters, the electrode with a diameter of 5 mm achieved the best particle collection efficiency (87.4%) at 900 K. The applied voltages of the electrodes with different intervals were almost similar, but the discharge currents varied significantly. The best particle collection efficiencies were achieved by the electrode with an interval of 55 mm at 300 K and 500 K, but at 700 K and 900 K, the electrode with an interval of 110 mm obtained the best result. The interval between electrodes should be expanded with an increase in temperature to avoid the offsetting of electric field between neighboring electrodes. [ABSTRACT FROM AUTHOR]

High-temperature electrostatic precipitators for removing dust from fuel or flue gases were proposed to improve energy efficiency or to avoid damaging downstream equipment. This paper attempts to provide a comprehensive understanding of negative DC corona discharges and find ways to increase corona stability at high temperatures. The characteristics of corona discharges were studied in a wire–plate discharge configuration under different discharge gaps and electrode geometries at temperatures ranging from 293 K to 1173 K. The V – I characteristics were analyzed, including corona onset/spark voltages, operating voltage ranges, and corona current compositions. The discharge current density increases as the temperature increases, and the electron-carried current becomes significant at high temperatures. For example, the electron-carried current makes up ∼40% of the total discharge current at 1073 K under an applied voltage of 10 kV. The applied voltage range decreases as the temperature increases. The corona discharges become unstable, and localized breakdowns occur frequently when the temperature exceeds 1073 K and the discharge gap is less than 50 mm, because the ionization coefficient and the number of electrons greatly increase. The operating voltage range increases from 8.2 kV to 13.6 kV at 1073 K when the discharge gap increases from 30 mm to 70 mm. Compared with the wire and spiral electrodes, the ribbon electrodes produce sparks more easily. The wire diameter has little influence on the spark voltage and corona stability at high temperatures. [ABSTRACT FROM AUTHOR]

• A novel-designed current measurement system contained 171 probes was designed. • The evolution of electric characteristics under various conditions was analyzed. • The current density distribution along the airflow direction was presented. • Some suggestions for relieving corona suppression were proposed. The high emission of SO 3 or sulfuric acid aerosol became a new environmental issue and has attracted international concerns. The sulfuric acid aerosol could be removed through droplet charging and transportation in the electric field. However, the charged droplets also have a converse effect on the electrostatic field. In this study, a novel-designed current measurement system contained 171 probes was designed to automatically scan and record the current density distribution along the airflow direction. Results show that the average current density was reduced by 31.3 % when SO 3 concentration was increased from 0 to 53.6 mg/m3, and the current density of the first electrode was only accounted for 11.3 % of the original current. A higher corona onset voltage was required to ionize the flue gas because of a reverse electric field formed by the charged droplets. The current density was also decreased with the flue gas velocity under the SO 3 presence condition. When the flue gas velocity reached 4 m/s, the corona suppression was severe and the inflection point was no longer obvious. The region that the relative current density below 0.6 was comprised 70 %. The current density could be enhanced by increasing the spike length and decreasing the spike spacing. The larger the corona current of the discharge electrode, the less the effect of the particle space-charge. Meanwhile, some suggestions for relieving corona suppression by enhancing the corona discharge at the inlet and promoting the droplet growth were proposed. [ABSTRACT FROM AUTHOR]

• A modified wet ESP model was established to study the particle space-charge effect. • The role of ultrafine particles in collection performance was investigated. • A combined wet ESP was developed and compared with the common wet ESP. • The correlation between precharging and particle charging was analyzed. • The contribution of precharging to particle precipitation was quantified. The collection performance of wet electrostatic precipitators (ESPs) considerably deteriorates in the presence of ultrafine particles, which confer difficulties in realizing the ultra-low emission of particulate matter (PM). In this work, the use of a wet ESP combined with a perforated precharger was proposed to investigate its electrical and collection characteristics in flue gas containing ultrafine particles and compared these characteristics with those of the common wet ESP. Results indicated that the distributions of ion density and electric field were affected by ultrafine particle loadings. With increased PM 0.1 concentration from 0 mg/m3 to 100 mg/m3, the average ion density of the common wet ESP decreased by more than two orders of magnitude. Meanwhile, the particle charging and transport performance deteriorated, even for large particles (10 μm), and migration velocity sharply decreased by more than 85 %. The corona electrostatic field was significantly improved by installing the precharger. The combined wet ESP can be operated well even under problematic conditions. Additional electrons were generated by the corona discharge of the precharger, which contributed to subsequent particle capture. When the applied voltage of the precharger exceeded 15 kV, the electrostatic precipitation of 1 μm particles only slightly weakened with increased PM 0.1 concentration to 40 mg/m3, and the capture of >5 μm-diameter particles was nearly unaffected by ultrafine particles. [ABSTRACT FROM AUTHOR]

The high-temperature electrostatic precipitator (ESP) is a potentially efficient method for hot-gas cleaning in advanced technologies, e.g., the coal-staged conversion poly-generation system and IGCC. This paper investigates the characteristics of the ash layer on the internal surface of the anode pipe of a wire–cylinder ESP at temperatures ranging from 350 °C to 700 °C, including ash deposition forms, growth of ash layer and the effect of ash layer on back corona discharge. There are four typical ash deposition forms: the belt form, the slope with ribs form, the slope form and the slope with a thick bottom edge form. Ash layer thickness generally decreases with increasing height. When T ⩽ 500 °C, ash belts form under low port voltages, and with increasing port voltage, they will overlap each other to form ash ribs. When T ⩾ 500 °C, particles are deposited in the smooth slope form if the port voltage is great enough. When T ⩾ 700 °C, a thick bottom ash edge occurs. Ash deposition forms can vary under different operating conditions. As the operating time increases, the thickness growth rate at a given point decreases, and the ash layer height increases because of the repulsive electrical force between the ash layer and the particles. Back corona discharge always occurs on the thickest portion of the ash layer first. The back corona discharge onset voltage decreases nearly linearly with increasing ash layer thickness, from 19,787 V to 17,197 V as the maximum thickness of the ash layer increases from 0.34 to 2.02 mm when T = 500 °C, U p = 17,200 V and m in = 650 mg/N m 3 . [ABSTRACT FROM AUTHOR]