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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]

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]

Electric agglomeration is a useful method to improve fly-ash particle collection efficiency in traditional electrostatic precipitators (ESPs) by increasing particle diameter and achieving particle pre-charging. In this study, a laboratory agglomerator, which consisted of a pre-charging region and a static mixer, was designed and tested for fine particle agglomeration. The pre-charging provided both positive and negative discharges in parallel channels. Fine water droplets were used to enhance particle agglomeration and collection efficiency in a downstream small ESP. The operating effects were evaluated under various applied voltages and droplet concentrations. Experimental results showed that the presence of water droplets effectively improved coal-fired particle agglomeration, pre-charging, and collection in the ESP. The total number collection efficiency improved from 53.91% to 86.02% compared with the condition without the agglomerator. In addition, a novel sampling method was used to observe agglomerated particles using scanning electron microscopy, and theoretical adhesive force analysis supported the proposal of a series of power-plant particle electric agglomeration modes. [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]

The severe current reduction and a significant drop in collection efficiency appear when containing ultrafine particles. In this study, a comprehensive model was developed to investigate the role of optimizing the corona wire arrangement in the electrostatic precipitator (ESP) performance enhancement. The total current increased initially and then decreased with the increase in wire-wire distance (without PM 0.1). The decrease in the wire-plate distance could enhance the corona discharge. The collection efficiencies for 1, 2.5, and 5 μm enhanced by 58.1%, 45.2%, and 37.4% when the wire-plate distance decreased from 300 mm to 100 mm (without PM 0.1), respectively. Compared with the wire-wire distance optimization, the ESP performance enhancement was more obvious for wire-plate distance optimization when containing ultrafine particles. The collection efficiency of 5 μm particles could increase by 323.2% when the PM 0.1 concentration reached 50 mg/m3. Meanwhile, some potential methods were proposed to improve ESP performance in treating ultrafine particles. [Display omitted] • A comprehensive model considered particle space-charge was developed. • The role of corona wire arrangement in corona discharge and particle motion was quantified. • Variation of ESP performance when containing ultrafine particles was analyzed. • Some potential methods were proposed to relieve corona suppression. [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]

• Multi-field modeling on simultaneously removing mercury and particulate matter. • The mass transfer module shows relatively higher accuracy than previous models. • Sorbent particle size predominates over simultaneous removal efficiency. • The influences of other typical operating parameters are carefully discussed. • EHD conditions have complex effects on capture of mercury and particulate matter. A computational fluid dynamics (CFD) model coupled with gas-particle mass transfer, electrohydrodynamic (EHD) effect, electric field, particle motion and particle charging is established to advance the understanding of combined particulate matter precipitation and mercury capture within industrial electrostatic precipitators (ESPs). The comparisons between experimental data and numerical results demonstrate that this model can reasonably predict the mercury removal efficiency by powdered sorbent injection (PSI). The mechanism of simultaneous removal of mercury and particulate matter is then discussed in detail by considering the complex interactions among multi-physics. The influences of particle size, mercury concentration, particle injection rate and the EHD effect are investigated. The simulation results indicate that the mercury removal process is primarily controlled by the sorbent particle residence time, surface area and mass transfer rate. Accordingly, reducing the size of sorbent particles (activated carbon) can promote mercury removal efficiency while decreasing the particle collection efficiency. Increasing the initial mercury concentration and adsorbent mass loading also benefit mercury adsorption by influencing the mass transfer rate and the surface area. The EHD effect plays important roles in mercury removal and particle collection by means of altering the flow patterns and particle migration. The two mechanisms of in-flight and wall-bounded mercury adsorption affected by ionic wind are also evaluated and some interesting phenomena are observed. [ABSTRACT FROM AUTHOR]

The electrostatic precipitator is widely used in many industries, such as power plants, waste incineration and glass production. The optimization of electrode and collecting plate is important for higher efficiency in electrostatic precipitator. In this work, the simulation results of electrical characteristics, particle charge, migration velocity and collection efficiency in four electrode configurations and two shaped collecting plates are presented. The results show that the distributions of the electric field and current density are different in each electrode and plate configuration. Sharpness of the discharge needle wire (NW) can simply lead to the high peak value of the electric field strength near the electrode wire surface. The concave-convex structure of the collecting plate can easily generate high current density near a corner of the BE collecting plate. The particle migration velocity and relative collection efficiency are calculated within eight different electrode-plate combinations. The BE collecting plate and needle wire electrode (BENW) configuration has the highest collection efficiency. The implication of the results in practice is discussed on this basis. Unlabelled Image • The effects of electrode wires and plates on ESP performance were studied numerically. • The electrical characteristics and particle transports were examined under different configurations. • The optimum electrode-plate configuration was identified under certain conditions for practice. [ABSTRACT FROM AUTHOR]

Electrostatic precipitators (ESPs) separate particles from flue gas by corona discharge and accompany by the generation of ionic wind. In this work, a Computational Fluid Dynamics model was presented to investigate the effects of ionic wind on flow field and particle precipitation in a honeycomb ESP in terms of the coupled processes among corona discharge, gas flow, particle charging and transport. Results indicated that the electric field and ion charge density around the needle tips were highest and respectively reach 2.5 × 106 V/m and 0.164 C/m3 in the gas without suspended particles, which played a key role in corona-electrostatic field. The maximum velocity of ionic wind could reach 13.81, 11.74 and 9.42 m/s under the applied voltage of 27, 21 and 15 kV, and ionic wind velocity sharply decreased away from the needle tip. Meanwhile, the flow field could be divided into three regions (ionic wind affected region, vortex and back flow region) according to the direction of gas flow velocity. When the electrically neutral particles with a spherical shape were injected into ESP at the entrance, the charged particles were transported by drag force and electric force, and inhomogeneous distribution of the deposited particle has occurred because of ionic wind. More intense vortices were formed with the increase in applied voltage, and promoting the particle precipitation process. Moreover, higher applied voltage enhanced the aggregation of particles in the upstream, and reduced the dead zone of deposited particles in the downstream. The ionic wind generated by corona discharge strongly disturbed the flow field and particle precipitation process. Image 1 • A 3D spike-honeycomb ESP model was established to study the role of ionic wind. • The distributed pattern of the electric field and ion charge were investigated. • High velocity ionic wind was generated near the tips and could reach 13.81 m/s. • The flow field of gas phase was divided into three regions because of ionic wind. • The correlation between the ionic wind and particle precipitation were analyzed. [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]