Collection Efficiency Of Submicron Particles Research Articles

Enhancing the sub-micrometer performance of a uniflow cyclone separator using a built-in stainless steel mesh filter

Although the uniflow cyclone separator has low pressure drop and high collection efficiency compared to other existing cyclone separators, it still has room to improve its collection efficiency of submicron particles. For this reason, we present a new uniflow cyclone separator with an installed mesh filter called the MFUC. The MFUC cyclone body is not made of a solid wall but a stainless steel mesh with porosity. Our research newly revealed that the pressure gradient in the radial direction at the front region of the mesh filter is reversed in the rear region, which can help to remove sub-micrometer particles which are difficult to collect using a basic cyclone separator. The measured MFUC performance showed the synergetic effect of filtration and inertial separation for the removal of fine particles. As the inlet flow rate increases, the inertial separation becomes more effective than filtration. In addition, the cut-off diameter of the MFUC was 0.83 μm at 500 lpm, which is 56.6 % smaller than that of the basic cyclone separator.

Experimental investigation of the effect of collection length in a two-stage electrostatic precipitator for removal of PM2.5

• The effect of collection length in a two-stage ESP was investigated in detail under consideration of various factors. • The collection efficiency of sub-micron particles could reach up to be more than 95% at 4 m/s gas velocity. • The sequence of the influence degree of main parameters in governing ozone concentration was obtained. In this work, a laboratory-scale charger, with a single wire electrode of one charging unit for effective ozone control, and collector with a 300 mm length and 5 mm plate-plate distance extremely short for high-efficient capture of noxious particles, was designed and assembled as a two-stage ESP to study the effect of collection length for removal of PM2.5, in particular to these sub-micron particles which had the highest penetration rate during the electrostatic capture process. The influence factors, including the current density of charger, the electric field strength of collector, and gas velocity, were investigated in detail. Multiple channels of the collector were chosen to thoroughly compare the performance difference by detecting the particle concentration in the electric field directly. Besides, the ozone concentration test was carried out in various parameters to explore the influence degree simultaneously. Experimental results showed that the collection efficiency based on the number concentration could reach up to be 92.9%, 96.7%, and 97.7% for 0.25 μm, 0.35 μm, and 0.45 μm diameter particles at 4 m/s gas velocity, respectively, which benefited from the advantages of long collection plate and short migration distance. Compared with the influence factors of charger current density and gas velocity, electric field strength occupied the middle position in effecting the collection efficiency, whose most massive index factor was about 18 at a collection length of 30 cm. While the maximum index factor of current density was 3.7 at a collection length of 15 cm and of gas velocity was 27.5 at a collection length of 10 cm. The ozone concentration test suggested that charger current, gas velocity, collection length, and electric field strength could affect the ozone concentration from strong to weak in sequence.

Charging effect on separation performance of outer vortex type cyclone for submicron particles at different operating parameters

Eliminating fine particles from flue gas is of vital importance to improve air quality, so an outer vortex type electrocyclone (EC) designed with corona wires was built and used to trap submicron particles. Besides, a mathematical model under multi-field coupling effect was established and the charging effect rule on collection efficiency of submicron particles was revealed by comparing the performance of electrocyclone with cyclone and changing operating conditions. The results indicate that the application of charging effect greatly reduces the escape of submicron particles, making that the collection efficiency in EC is far higher than the one in cyclone. Compared to the cyclone, the ability of charging effect to promote the separation performance of EC increases with the increasing working voltage and the decreasing flue gas velocity and temperature and the trapping performance is better at a higher working voltage, lower flue gas velocity, and lower temperature. Furthermore, for outer vortex type EC, the charging effect is more prominent with the decrease of working voltage, flue gas velocity and temperature. The obtained results were evaluated to provide a reliable guide for designing an outer vortex type EC, thus greatly decreasing the number of tests and effectively reducing the research cost.HighlightsA physical model of outer vortex type cyclone with corona wires was built.A theoretical model with four-field coupling interaction is established.The charging effect on collection efficiency of submicron particles is explored.Charging effect can availably improve the separation performance of cyclone.Charging effect is more prominent at lower voltage, flue velocity, and temperature.

Experimental study on electrostatic removal of high-carbon particle in high temperature coal pyrolysis gas

A high-temperature electrostatic precipitator (ESP) presents a good solution for hot gas cleaning, which can remove fly ash from pyrolysis gas at temperatures higher than the tar dew point. In this paper, the characteristics of negative DC corona discharge in air and simulated coal pyrolysis gas were studied. The removal of coal pyrolysis furnace fly ash (ash A) was investigated and compared with that of coal-fired power plant fly ash (ash B) in ESP with a temperature ranging from 300 K to 900 K. The current density of simulated gas was higher than that of air under the same discharge voltage and at different temperatures. The simulated gas also had a higher spark voltage and a lower onset voltage compared with air. The fractional collection efficiency of ash A was lower for particles with diameters of larger than 0.1 µm at high temperature, compared with ash B. A lower collection efficiency in simulated gas was obtained for particles with diameters of less than 0.1 µm compared with air. The collection efficiency of submicron particles in simulated gas was usually higher than it in air, especially for particles with diameters of less than 0.04 µm. In simulated gas, the overall collection efficiency of ash A was obviously lower than that of ash B, especially at high temperature. From 300 K to 700 K, the collection efficiencies of both ash samples were as high as above 93%, but the collection efficiency of ash A in simulated gas decreased to 78.7% at 900 K.

Particle Collection Efficiency of Polypropylene Nonwoven Filter Media Charged by Triode Corona Discharge

The aim of this paper is to evaluate the collection efficiency of submicron particles using electrically charged nonwoven filter media. A triode-type electrode arrangement consisting of a high-voltage wire-type ionizing electrode, a metallic grid, and grounded plate electrode is employed to control the distribution of electric charges deposited on the media. Surface electric potential measurement is carried out to study the evolution in time and the repartition in space of deposited charges. The collection efficiency is estimated by measuring the particle concentrations downstream and upstream of the charged filter media. The main results show good correlation between the surface potential level and the collection efficiency of submicron particles for several charging conditions. In particular, filtration performance increases with increasing the corona current through the media during the charging process. Increasing the electric field between the grid and the media during corona charging has also a positive effect on the collection efficiency. Results indicate that high collection performances could not be achieved using thin monolayer media.

Numerical study of pressure drop and diffusional collection efficiency of several typical noncircular fibers in filtration

Noncircular fibers have larger specific surface area compared to the circular cross-section fiber with the same volume fraction and may perform higher collection efficiency of submicron particles. In this article, we use a lattice Boltzmann-cellular automata (LB-CA) probabilistic model to simulate the particle filtration processes of four kinds of noncircular fibers with rectangular, trilobal, quatrefoil and triangular cross-sections at low Reynolds number (less than 1). The pressure drop and collection efficiency for the diffusion dominant regime, where the Peclet number ranges from 235 to 1000, are investigated. By normalizing the pressure drop and collection efficiency of noncircular fibers with those of the circular fiber, which can be calculated from the existing classical expressions developed in the past, the corresponding ratios are gained. Then the Levenberg–Marquardt algorithm is used to obtain the fitting expressions of the above ratios. The proposed easy-to-use fitting expressions can be used to calculate the pressure drop and diffusional collection efficiency of noncircular fibers under different operation conditions, when the fiber volume fraction is 5%–10%. The results show that the pressure drop of noncircular fibers is dependent on the orientation angle and the aspect ratio. The diffusional collection efficiency is almost independent of the orientation angle but proportional to the aspect ratio for all the noncircular fibers.

Centrifugal Filter for Aerosol Collection

Air filters collect particles by the mechanical collection mechanisms, namely, inertia, interception, gravitational settling, and Brownian diffusion. There exists the most penetrating particle size (MPPS) in submicron size range for which none of the collection mechanisms work effectively. In this study, we propose a new type of filter named as “centrifugal filter,” which collects aerosol particles by centrifugal force together with the conventional mechanical collection mechanisms. The centrifugal filter proposed in the present work may be rotated by a motor or compressed air. Air passes through the filter in the axial direction of filter rotation. The filter rotates so does the air embedded in the filter, and therefore centrifugal force exerts on particles. In addition to the mechanical collection mechanisms, small migration of particles due to the centrifugal force enhanced the collection efficiency of submicron particles significantly without increasing the pressure drop. The performance tests of cent...

Systematic Approach to Optimization of Submicron Particle Agglomeration Using Ionic-Wind-Assisted Pre-Charger

Electric agglomeration is the process in which particles are charged in electric fields and coagulate, which is enhanced by electric force or turbulence. The collection efficiency of submicron particles is improved, which can be a solution to submicron particle abatement in traditional electrostatic precipitators (ESPs), by using a pre-charger to increase median particle diameter and realizing particle pre-charging. In this study, a laboratory bipolar pre-charger with a perforated plate between discharging regions was designed to examine ionic-wind-assisted charge-induced agglomeration, and an ESP was arranged afterwards to collect the fine particles. Experiments were conducted to investigate submicron particle charging, agglomeration characteristics, and collection efficiency. Results indicated that a pre-charger with proper discharging voltage match and plate porosity can optimize particle agglomeration and improve collection efficiency by about 12% compared with the results obtained without a pre-charger. An optimal solution was achieved and a collecting efficiency of 96%–98% was obtained for all sizes by utilizing the turbulence caused by ionic wind and optimizing the experimental operation conditions.

Use of Pulse-Energized Electrostatic Precipitator to Remove Submicron Particulate Matter in Exhaust Gas

An electrostatic precipitator (ESP) with negative pulse corona discharge for removal of submicron particles in the exhaust gas of thermal equipment such as boilers, burners or internal combustion engines is presented. A wire-cylinder ESP was designed and constructed for experimental testing at laboratory scale. The collection efficiency of submicron particles in the exhaust gas of a diesel burner under various dust loadings and gas velocities was investigated. The results were compared with those obtained from the conventional DC ESP technique. It was found that the pulse peak voltage supply could be set much higher than the sparking limit of the DC energized unit. Thus, the electric field density could be increased, which resulted in a higher collection efficiency. The higher pulse frequency also increased the collection efficiency, especially for submicron particles.

Effects of thermophoresis, vapor, and water film on particle removal of electrostatic precipitator

The effects of thermophoresis, vapor, and water film on the collection efficiency of wet electrostatic precipitators (wet ESPs) were experimentally investigated. The results showed that the fractional collection efficiency curve on the influence of thermophoresis, vapor, and water film was similar to that of traditional ESPs, which exhibited the minimum value at particle diameters of about 0.5μm. Thermophoresis was beneficial to the collection efficiency of ESPs but the promotion of collection efficiency was not obvious due to the suppression of the ion current caused by lower gas temperature. Vapor significantly improved the collection efficiency of small particles (with diameters smaller than 0.2μm). However, it had little effect on the removal of large particles (those with diameters over 2μm). When water was injected into the wet ESP, water film formed on the surface of the collection electrode greatly improved the collection efficiency of submicron particles and it also promoted the removal of large particles significantly. The effect of the water film on the collection efficiency of wet ESPs was a combined result of thermophoresis, vapor, and water flushing.

Modeling of Gravitational Wet Scrubbers with Electrostatic Enhancement

AbstractConventional gravitational wet scrubbers, which generally perform removal of fine particles with low efficiency, cannot meet new standards for pollution emissions. One way of improving the collection efficiency of fine particles is to impose additional electrostatic forces upon particles by means of particle‐charging, or droplet‐charging, or even opposite‐charging of particles and droplets. A Monte Carlo method for population balance modeling is presented to describe the particle removal processes of gravitational wet scrubbers with electrostatic enhancement, in such a way that the grade collection efficiency and particle size distribution are calculated quantitatively. Numerical results show that, the grade collection efficiency of submicron particles is only ca. 5 % in conventional wet scrubbers. However, it reaches ca. 25 % in particle‐charging wet scrubbers, ca. 70 % in droplet‐charging wet scrubbers, and even above 99 % in opposite‐charging wet scrubbers. Furthermore, population balance modeling is used to optimize the operational parameters of the droplet‐charging wet scrubbers by means of the quantitative comparison of the grade collection efficiency. It is found that the operational parameters that are beneficial to the high‐efficiency removal of fine particles are faster gas velocity, slower droplet velocity, larger liquid‐to‐gas flow ratio, larger charge‐to‐mass ratio of droplets, smaller geometric mean diameter and smaller geometric standard deviation of droplets.

Characteristics of electrostatic cyclone/bag filter with inlet types (lab and pilot scale)

The main purpose of this study was to investigate experimentally the characteristics of an electrostatic cyclone/bag filter with inlet types (upper and bottom inlet) in order to overcome the low collection efficiency for submicron particles and high pressure drop, which were the main problems of general fabric bag filters. The experiment was performed to analyze the collection efficiency and pressure drop of the electrostatic cyclone/bag filter compared with that of conventional fabric bag filters with various experimental parameters such as the inlet type (upper and bottom), inlet velocity (filtration velocity) and applied voltages. From the results, the upper inlet type showed a slightly higher pressure drop reduction ratio as 40–90% than that of bottom inlet. In addition, the electrostatic cyclone/bag filter represented an increment of over 5% for the collection efficiency of submicron particles (around 1 Μm) in comparison with the general fabric filter.

Test of Mathematical modeling for performanceof conduit type scrubbers

A mathematical model has been developed for the prediction of the collection efficiency of submicron particles in the conduit type scrubber. A pilot scale plant has been used for testing the mathematical model. Submicron particles have been generated by spraying solution of Methylen Blue. The distribution of particles has been measured by an Electrical Aerosol Size Analyzer. The model has been tested by the experimental data and good agreement between predicted values and experimental data have been observed.

Collection efficiency of submicron particles and pressure drop measurements in grid filters

The particle collection efficiencies and pressure drops across model grid filters were measured as a function of particle diameter, filter thickness, and gas velocities. The experimental velocities, ranging from 20 to 600 cm/sec, covered regions where diffusion was dominant and where re-entrainment was significant. Three particle sizes — 1.01 μm. 0.79 μm and 0.36 μm — were used in this study. A simple model of “channeling”, based solely on geometric considerations, was used to calculate single fiber efficiencies. These values were found to be independent of filter thickness. The model was confirmed by electron micrographs. The pressure drop measurements were correlated with the Fuchs—Stechkina equation with C* ⋍ 0.51 for argon and C* ⋍ 0.53 for methane. Electron micrographs suggest a broad particle deposition pattern that must be accounted for in subsequent calculations. Theoretical predictions of the particle deposition patterns on the fibers using the Happel cell model did not agree with counts from the photographs. The deposition formed a broad band on the fiber in contrast to the predicted narrow band.