Search

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]