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High-temperature ESPs are proposed to improve energy efficiency and avoid damage to downstream equipment in integrated gasification combined cycle and pressurized fluidized-bed combustion. In this study, the effects of temperature and pressure on negative corona discharge characteristics were compared. Gas temperature varied from 373 K to 1073 K, and pressure varied from 30 kPa to 100 kPa to achieve the same gas density. The additional corona current Δ I t induced by high temperature was calculated, and the additional ion current Δ I i and electron current Δ I e were studied. A wire-type electrode, a spiral electrode, a ribbon electrode, and four gas compositions (N 2 /CO 2 /SO 2 /air) were investigated in the plate-type discharge configuration. Results show that corona current increases more rapidly with increasing gas temperature than that with decreasing pressure at the same gas density. The current density is 0.87 mA/m at 973 K and atmosphere pressure, which is higher than 0.45 mA/m at 30.9 kPa and room temperature. An additional temperature effect on corona discharge is proposed apart from the decrease of gas density as temperature increases. Δ I t increases with increasing temperature because of enhanced molecule kinetic energy and ionization rate. The electron-carried current is important at temperatures above 873 K. Δ I e /Δ I t increases from 0 to 0.941 when temperature increases from 773 K to 973 K. Compared with the Δ I t of wire and spiral electrodes, the Δ I t of ribbon electrode is significantly larger because of the enhanced electron avalanche and secondary electron emission. Negative corona discharge does not occur in N 2 , and corona onset voltages are in the following sequence: CO 2 > SO 2 (6000 ppm) > air, which is determined by gas molecule ionization energy. Δ I t / I P is smaller in gas atmosphere with strong electronegativity. [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]

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]

An experimental-scale electrostatic precipitator (ESP) was built to investigate the characteristics of corona discharge, particle migration, and particle collection at various temperatures ranging from 300 K to 900 K. The variations in particle collection efficiencies and migration velocities with temperature, applied voltage, current density, energy consumption density, particle concentration, and flue gas velocity were obtained. Both onset and spark voltages decreased with an increase in temperature and resulted in a decrease in particle collection efficiency and particle migration velocity. At the same voltage, a large current was generated at high temperature; particle charging was enhanced, and high particle collection efficiencies and particle migration velocities were obtained. At the same current and energy consumption densities, the particle collection efficiencies decreased because of the low electric field intensity. The increase in particle concentration was favorable to particle collection and improved the particle migration velocities. The increase in flue gas velocity reduced the particle collection efficiencies and had minimal influence on the particle migration velocities. [ABSTRACT FROM AUTHOR]