Search

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]

High-temperature electrostatic precipitation is a potential method for hot gas clean-up that is hindered by the issue of back corona discharge (BCD). This paper reports on the development of BCD at 350–700 °C in a wire-cylinder electrostatic precipitator (ESP). As the output voltage of power supply increases, BCD begins at the surface of the ash layer, and then it extends toward the electrode gap space, forming consecutive discharge channels that bridge the two electrodes, ultimately leading to spark breakdown (SB). The discharge process that follows BCD can be classified into different stages: the NCD & BCD stages, the weak NCD, BCD & glow discharge stage, and the BCD & SB stages. At high temperatures (500 °C or above), BCD is likely to convert to SB. In the NCD & BCD stages, the collection efficiency of the electrostatic precipitator is not affected, i.e., the collection efficiency is ~ 99.65%, regardless of whether BCD exists or not at a temperature of 350 °C and a port voltage of ~ 17,200 V. In the BCD & SB stages, the collection efficiency is greatly reduced, i.e., it is ~ 88.35% in the NCD-only stage at a temperature of 500 °C and a port voltage of ~ 14,000 V, whereas it is only ~ 67.42% in the BCD & SB stages. It should be noted that BCD results in an increase in the power consumption of the ESP for all stages. A physical model is proposed to explain the processes that initiate, maintain, and develop BCD. [ABSTRACT FROM AUTHOR]

Abstract: High temperature combustion experiments of waste printed circuit boards (PCBs) were conducted using a lab-scale system featuring a continuously-fed drop tube furnace. Combustion efficiency and the occurrence of inorganic bromine (HBr and Br2) were systematically studied by monitoring the main combustion products continuously. The influence of furnace temperature (T) was studied from 800 to 1400°C, the excess air factor (EAF) was varied from 1.2 to 1.9 and the residence time in the high temperature zone (RTHT) was set at 0.25, 0.5, or 0.75s. Combustion efficiency depends on temperature, EAF and RTHT; temperature has the most significant effect. Conversion of organic bromine from flame retardants into HBr and Br2 depends on temperature and EAF. Temperature has crucial influence over the ratio of HBr to Br2, whereas oxygen partial pressure plays a minor role. The two forms of inorganic bromine seem substantially to reach thermodynamic equilibrium within 0.25s. High temperature is required to improve the combustion performance: at 1200°C or higher, an EAF of 1.3 or more, and a RTHT exceeding 0.75s, combustion is quite complete, the CO concentration in flue gas and remained carbon in ash are sufficiently low, and organobrominated compounds are successfully decomposed (more than 99.9%). According to these results, incineration of waste PCBs without preliminary separation and without additives would perform very well under certain conditions; the potential precursors for brominated dioxins formation could be destroyed efficiently. Increasing temperature could decrease the volume percentage ratio of Br2/HBr in flue gas greatly. [Copyright &y& Elsevier]

A spiral solar particle receiver (SSPR) with a conical cover was proposed, and the performance was experimentally and numerically investigated. The SSPR was heated by a concentrated radiant flux of ∼5 kW over a 10 cm-diameter aperture with a maximum irradiance of over 700 kW/m 2 . The experimental results indicated the particle temperature increase reached over 625 °C in a single pass with an optical and a thermal efficiency of ∼87% and ∼60%, respectively, when the mass flow rate was 0.21 kg/min. The optical performances of the solar simulator and the receiver were combined and simulated by the Monte-Carlo ray-tracing method. Based on the optical model, a dynamic thermal conversion model was built, which indicated the particle temperature and the overall efficiency of SSPR would reach 628–673 °C and 58.9–63.7%, respectively, when the SSPR was coupled with a 3 m two-stage dish concentrator with a solar inclination angle ranging from 60° to 120°. [ABSTRACT FROM AUTHOR]

The flue gas generated from glass furnaces contains particles with high concentrations of alkali metals and hazardous heavy metals, which could reduce the lifespan of selective catalytic reduction (SCR) catalysts and lead to catalyst deactivation. Removing the particles before SCR could improve system operation reliability and reduce nitric oxides (NOx) emission. In this paper, the characteristics of fly ash from glass furnaces and the particle removal properties in the electrostatic precipitator (ESP) from 363 K to 623 K were studied. The particle collection efficiency was found to decrease with increasing temperature. A method of enhancing particle removal was proposed and tested through particle conditioning in a lab-scale experiment. In order to change the characteristics of the fly ash, calcium carbonate powders were used as conditioning particles and the particle collection efficiency increased from 65.8% to 87.6% at 623 K. This method was further applied in an industrial high-temperature ESP for a glass furnace. When the ratio in mass between the particles from the glass furnace and from the conditioning proportion was 1:1.5, the particle collection efficiency of the ESP was improved significantly and the outlet particle concentrations decreased from 103.23 mg/Nm 3 to 39.25 mg/Nm 3 . [ABSTRACT FROM AUTHOR]

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 precipitation is a potentially convenient method for hot gas clean-up. This paper reports the characteristics of electrostatic precipitation in a wire–cylinder configuration for a temperature range of 350 °C to 700 °C. Three parameters, i.e., particle collection efficiency, energy consumption index and the outlet mass concentration of particles, are investigated to evaluate the comprehensive performance of an electrostatic precipitator at high temperatures and to propose a method to choose an optimum combination of the operation parameters for different conditions. The collection efficiency can be greater than 0.996 when the gas temperature is 350–700 °C and the inlet mass concentration of particles is 200–3600 mg/Nm 3 . When the voltage applied to the two electrodes is high enough (greater than 15,900 V in this work), the collection efficiency is hardly influenced by the inlet mass concentrations of particles in the testing range. For example, at 620 °C when the applied voltage is 15,925 V, the fluctuations of the collection efficiency are within ~ 0.2% even if the inlet mass concentration increases ~ 10 times. For a given inlet mass concentration of particles, the collection efficiency increases rapidly as the applied voltage increases from the first stage to the second stage, while the collection efficiency increases slowly as the applied voltage increases from the second stage to the third stage. The relationship between the energy consumption index, the applied voltage and the inlet mass concentration of particles is given by φ = CU p 2 ( U p − U c )/ m in . As the temperature increases from 350 °C to 700 °C, the value of C increases from 1.0 × 10 − 5 to 3.2 × 10 − 5 and the value of U c decreases from 20,860 to 12,503. The electric energy consumed by an electrostatic precipitator increases rapidly with the increase in the temperature. [ABSTRACT FROM AUTHOR]

Abstract: To study the characteristics of DC negative corona discharge in a wire-cylinder configuration at an ambient temperature range of 350–850 °C, the I–V characteristics and the current composition are analyzed under different conditions. A simple method is proposed to determine the DC corona onset threshold voltage. At high ambient temperatures, in the DC negative corona discharge gap, some electrons are not attached to the electronegative gas molecules and move to the anode tube. Thus, these electrons form an electron current, which may account for most of the total discharging current. The ratio of the electron current to the total discharging current increases with increasing temperature. In a mixture of O2 and N2 and a mixture of CO2 and N2, the ratio of electron current increases with increasing N2 content in the mixtures. The cathode material has little influence on the corona discharge characteristics at high ambient temperatures. [Copyright &y& Elsevier]

In the present work, the characteristics of direct-current (DC) discharge in a wire-cylinder configuration at an ambient temperature range of 350–850 °C were studied by analyzing photographs of the discharging process and the corresponding V–I characteristics, with the aim of facilitating the application of plasma technology in the fields of energy and the environment. The influences of the ambient temperature, the inter-electrode gap, the gas medium and the cathode material on the DC discharge were investigated. The corona-onset threshold voltage (COTV) and the spark-breakdown threshold voltage (SBTV) decrease as the ambient temperature increases, and the SBTV decreases more rapidly. Increasing the inter-electrode gap enlarges the difference between the SBTV and the COTV. After spark breakdown, in an air atmosphere, glow discharge is more likely to take place under conditions of high ambient temperatures or small inter-electrode gaps. The values of the SBTV in different atmospheres have the following relation: air ≈ O2 > CO2. At an ambient temperature range of 350–850 °C and in an atmosphere of N2, glow discharge and arc discharge occur successively as the output voltage of the power supply is increased, while in an atmosphere of O2 and CO2, only corona and arc discharge are successively observed. In an air atmosphere, when the inter-electrode gap is 29 mm, corona, glow and arc discharge occur successively with increasing output voltage when the ambient temperature is 850 °C, while only corona and arc discharge appear when the temperature is 350–750 °C. When the inter-electrode gap is 5 mm in an air atmosphere, corona, glow and arc discharge occur successively in an ambient temperature range of 350–850 °C. The cathode material has a minor influence on the COTV and a more significant influence on the SBTV. In a device using a cathode with a low work function, the SBTV is low, and the power to maintain arc discharge is small. [ABSTRACT FROM AUTHOR]