Fugitive dust emission source profiles and assessment of selected control strategies for particulate matter at gravel processing sites in Taiwan

Particles emitted from gravel processing sites are one contributor to worsening air quality in Taiwan. Major pollution sources at gravel processing sites include gravel and sand piles, unpaved roads, material crushers, and bare ground. This study analyzed fugitive dust emission characteristics at each pollution source using several types of particle samplers, including total suspended particulates (TSP), suspended particulate (PM10), fine suspended particulate (PM2.5), particulate sizer, and dust-fall collectors. Furthermore, silt content and moisture in the gravel were measured to develop particulate emission factors. The results showed that TSP (< 100 microm) concentrations at the boundary of gravel sites ranged from 280 to 1290 microg/m3, which clearly exceeds the Taiwan hourly air quality standard of 500 microg/m3. Moreover, PM10 concentrations, ranging from 135 to 550 microg/m3, were also above the daily air quality standard of 125 microg/m3 and approximately 1.2 and 1.5 times the PM2.5 concentrations, ranging from 105 to 470 microg/m3. The size distribution analysis reveals that mass mean diameter and geometric standard deviation ranged from 3.2 to 5.7 microm and from 2.82 to 5.51, respectively. In this study, spraying surfactant was the most effective control strategy to abate windblown dust from unpaved roads, having a control efficiency of approximately 93%, which is significantly higher than using paved road strategies with a control efficiency of approximately 45%. For paved roads, wet suppression provided the best dust control efficiencies ranging from 50 to 83%. Re-vegetation of disturbed ground had dust control efficiencies ranging from 48 to 64%.     

A Model to Predict the System Performance of an Electrostatic Precipitator for Collecting Polydisperse Particles

Abstract

This paper presents a model for predicting the performance of an electrostatic precipitator (ESP) for collecting polydisperse particles. The particle charge was obtained by modifying Cochet’s charge equation; the particle size distribution was approximated by a lognormal function; and then the statistic method of moments was employed to obtain a set of the first three moment equations. The continuous evolution of the particle size distribution in an ESP is easily taken into account by the first three moment equations. The performance of this model was validated by comparing its predictions with the existing data available in the literature. Effects of the particle size distribution on the ESP performance were examined, and the results indicated that both overall mass and number efficiencies are lower for inlet particles with a larger mass median diameter and a higher geometric standard deviation. The methodology introduced may be applied to develop design criteria and determine optimal operating conditions of an ESP for improving the collection efficiency of the submicron particles.     

Dust Collection Efficiency Analysis in a Two-Dimensional Circulating Granular Bed Filter

Abstract

Dust collection efficiency data were analyzed to determine better operating conditions for a two-dimensional circulating granular bed filter (CGBF). The dust collection efficiency in the granular bed was affected by the following operating parameters: the louver angle, the solids mass flow rate, and the particle size of the bed material. Experimental results showed that higher dust collection efficiency occurs when the solids mass flow rates were 20.34 ± 0.24, 21.50 ± 0.11, and 30.51 ± 0.57 g/sec at louver angles of 45°, 30°, and 20°, respectively. Optimal dust collection efficiency peaked with a louver angle of 30°. Average particle sizes of bed material by sieve diameters (μm) of 795 μm had higher dust collection efficiency than the average collector particle size of 1500 μm. Dust collection efficiency is influenced by bed material attrition phenomenon, causing dust collection efficiency to decrease rapidly. The dust collection efficiency analysis not only found the system free of design defects but also assisted in the operation of the two-dimensional CGBF system.     

Fugitive Dust Emission Source Profiles and Assessment of Selected Control Strategies for Particulate Matter at Gravel Processing Sites in Taiwan

Abstract

Particles emitted from gravel processing sites are one contributor to worsening air quality in Taiwan. Major pollution sources at gravel processing sites include gravel and sand piles, unpaved roads, material crushers, and bare ground. This study analyzed fugitive dust emission characteristics at each pollution source using several types of particle samplers, including total suspended particulates (TSP), suspended particulate (PM₁₀), fine suspended particulate (PM_2.5), particulate sizer, and dust-fall collectors. Furthermore, silt content and moisture in the gravel were measured to develop particulate emission factors. The results showed that TSP (<100 µm) concentrations at the boundary of gravel sites ranged from 280 to 1290 µg/m³, which clearly exceeds the Taiwan hourly air quality standard of 500 µg/m³. Moreover, PM₁₀ concentrations, ranging from 135 to 550 µg/m³, were also above the daily air quality standard of 125 µg/m³ and approximately 1.2 and 1.5 times the PM_2.5 concentrations, ranging from 105 to 470 µg/m³. The size distribution analysis reveals that mass mean diameter and geometric standard deviation ranged from 3.2 to 5.7 µm and from 2.82 to 5.51, respectively. In this study, spraying surfactant was the most effective control strategy to abate windblown dust from unpaved roads, having a control efficiency of approximately 93%, which is significantly higher than using paved road strategies with a control efficiency of approximately 45%. For paved roads, wet suppression provided the best dust control efficiencies ranging from 50 to 83%. Re-vegetation of disturbed ground had dust control efficiencies ranging from 48 to 64%.     

Dust collection efficiency analysis in a two-dimensional circulating granular bed filter

Dust collection efficiency data were analyzed to determine better operating conditions for a two-dimensional circulating granular bed filter (CGBF). The dust collection efficiency in the granular bed was affected by the following operating parameters: the louver angle, the solids mass flow rate, and the particle size of the bed material. Experimental results showed that higher dust collection efficiency occurs when the solids mass flow rates were 20.34 +/- 0.24, 21.50 +/- 0.11, and 30.51 +/- 0.57 g/sec at louver angles of 45 degrees, 30 degrees, and 20 degrees, respectively. Optimal dust collection efficiency peaked with a louver angle of 30 degrees. Average particle sizes of bed material by sieve diameters (microm) of 795 microm had higher dust collection efficiency than the average collector particle size of 1500 microm. Dust collection efficiency is influenced by bed material attrition phenomenon, causing dust collection efficiency to decrease rapidly. The dust collection efficiency analysis not only found the system free of design defects but also assisted in the operation of the two-dimensional CGBF system.     

Size Distribution of Participates Emitted from a Horizontal Spike Soderberg Aluminum Reduction Cell

Aerosol size distributions were measured in the air exhausted from a horizontal spike Soderberg aluminum reduction cell at the Kaiser Aluminum and Chemical Corporation plant in Tacoma, Wash. The particle size distributions were measured with the University of Washington cascade impactor, developed specifically for source testing. The particle mass concentrations and size distributions were found to vary significantly with changes in the cell process operations. For a typical aerosol size distribution at the exit of the cell hood the mass mean particle diameter was 5.5 microns and the particle size standard geometric deviation was 25.     

Technique for Measuring Dust Collector Efficiency As a Function of Particle Size

With a specially designed generator, producing an aerosol of concentration, chemical composition, and size distribution similar to incinerator aerosols, a scrubber was tested in the laboratory by sampling before and after the collector. Using an Andersen Sampler as a 7 stage cascade impactor the efficiency for 7 different size classes was determined. This technique provides a rapid and simple method for evaluating the performance of a collector as a function of particle size. The multistage impaction classifies the particles according to their aerodynamic behavior. Gravimetric analysis of each stage eliminates the need for tedious counting and sizing.     

Collection of Aerosol Particles by Electrostatic Droplet Spray Scrubbers

Theoretical calculations and experimental measurements show that the collection of small aerosol particles (0.05 to 5 micron diameter range) by water droplets in spray scrubbers can be substantially increased by electrostatically charging the droplets and particles to opposite polarity. Measurements with a 140 acfm two chamber spray scrubber (7 seconds gas residence time) showed an increase in the overall particle collection efficiency from 68.8% tit uncharged conditions to 93.6% at charged conditions, with a dioctyl phthalate aerosol (1.05 μm particle mass mean diameter and 2.59 geometric standard deviation). The collection efficiency for 0.3 μm particles increased from 35 to 87% when charged. During 1973–1974 a 1000 acfm pilot plant electrostatic scrubber was constructed inside a 40 ft trailer for evaluation on controlling particu-late emissions from pulp mill operations (funded by Northwest Pulp and Paper Association). Field tests performed on the particle emissions exhausting from SO₂ absorption towers treating the gases from a magnesium based sulfite recovery boiler have shown particle collection efficiencies ranging from about 60 to 99% by weight, depending on the electrostatic scrubber operating conditions. Energy requirements for the University of Washington electrostatic scrubber are about 0.5 hp/1000 acfm (350 Watts/1000 acfm) including gas pressure drop, water pressure drop, and electrostatic charging of the water spray droplets and the particles.     

Collection Efficiency as a Function of Particle Size,Shape and Density: Theory and Experience

The performance features of both industrial and experimental fabric filter systems with respect to the concentration and particle size properties of the collector effluents are examined. From a qualitative viewpoint the factors that should influence significantly the collection characteristics of a fabric filter are dust properties, fabric properties, operating parameters, filter cleaning method, and critical interdependencies. The quantitative prediction of performance and the establishment of design parameters are limited for a generalized approach but data have been reported that provide excellent support for limited applications.     

燃煤手烧锅炉除尘器的研究与开发

介绍了一种集多种湿法除尘技术之长于一体的新型组合式除尘装置,该装置不仅能有效地消除手烧锅炉燃烧时产生的烟尘,而且实现了除尘水的内循环,消除了其他湿式除尘器所带来的水的二次污染问题。     

燃煤手烧锅炉除尘器的研究与开发

介绍了一种集多种湿法除尘技术之长于一体的新型组合式除尘装置，该装置不仅能有效地消除手烧锅炉燃烧时产生的烟尘，而且实现了除尘水的内循环，消除了其他湿式除尘器所带来的水的二次污染问题。     

Optical measurements of aerosol size distributions in Great Smoky Mountains National Park: dry aerosol characterization

Aerosol size distributions were measured during the summertime 1995 Southeastern Aerosol and Visibility Study (SEAVS) in Great Smoky Mountains National Park using an Active Scattering Aerosol Spectrometer (ASASP-X) optical particle counter. We present an overview of the experimental method, our data inversion technique, timelines of the size distribution parameters, and calculations of dry accumulation mode aerosol density and refractive index. Aerosol size distributions were recorded during daylight hours for aerosol in the size range 0.1 < Dp < 2.5 microns. The particle refractive index used for the data inversion was calculated with the partial molar refractive index approach using 12-hr measured aerosol chemical composition. Aerosol accumulation mode volume concentrations ranging from 1 to 26 micron 3 cm-3 were observed, with an average of 7 +/- 5 micron 3 cm-3. The study average dry accumulation mode geometric volume median diameter was 0.27 +/- 0.03 micron, and the mean geometric standard deviation was 1.45 +/- 0.06. Using an internally mixed aerosol model, and assuming chemical homogeneity across the measured particle distribution, an average accumulation mode dry sulfate ion mass scattering efficiency of 3.8 +/- 0.6 m2 g-1 was calculated.     

The Mass Distribution of Large Atmospheric Particles

This paper describes the results of a study to determine the total mass and the mass distribution of atmospheric aerosols, especially that mass associated with particles greater than 10 μm diameter. This study also determined what fraction of the total aerosol mass a standard high-volume air sampler collects and what fraction and size interval settle out on a dust fall plate. A special aerosol sampling system was designed for this study to obtain representative samples of large airborne particles. A suburban sampling site was selected because no local point sources of aerosols existed nearby. Samples were collected under various conditions of wind velocity and direction to obtain measurements on different types of aerosols.

Study measurements show that atmospheric particulate matter has a bimodal mass distribution. Mass associated with large particles mainly ranged from 5 to 100 μm in size, while mass associated with small particles ranged from an estimated 0.03 to 5 μm in size. Combined, these two distributions produced a bimodal mass distribution with a minimum around 5 μm diameter. The high-volume air sampler was found to collect most of the total aerosol mass, not just that fraction normally considered suspended particulate. Dust fall plates did not provide a good or very useful measure of total aerosol mass. The two fundamental processes of aerosol formation, condensation and dispersion appear to account for the formation of a bimodal mass distribution in both natural and anthropogenic aerosols. Particle size distribution measurements frequently are in error because representative samples of large airborne particles are not obtained. Considering this descrepancy, air pollution regulations should specify or be based upon an upper particle size limit.     

Theoretical investigation of pressure drop in combined cyclone and fabric filter systems

Computer simulations were conducted to investigate potential pressure drop reductions obtainable by combining cyclones, as pre-collectors, with fabric filters. The Leith-Licht model was used to characterize cyclone emissions and the specific resistance (K₂) of the fabric filter dust cake was calculated from an empirical correlation. Several important dimensionless groups were identified and evaluated. One group, the product of the ratio of the dust cake specific resistances expected with and without the cyclone and the mass penetration of the cyclone, (K₂/K₂) Pn, indicates whether a pressure drop reduction is possible. A correlation was developed for this group as a function of the size properties of the inlet dust (particle mass median diameter and geometric standard deviation) and the cyclone particle cut diameter. Expressions were derived for the break-even time, the duration of filtration with the cyclone needed to show a pressure drop reduction in comparison with filtration without the cyclone. It is shown that in previously reported experiments and simulations indicating an advantage for the combined cyclone-fabric filter system, filtration cycles were typically longer than the break-even time; those showing no improvement typically had filtration times shorter than the break-even time.     

Evaluation of cyclone performance in different gases

A new set of the cyclone efficiency data is reported. The particle collection efficiency data have been obtained as a function of particle size, flow rate, cyclone size, and gas properties. Cyclones of four different dimensions were used covering a flow rate range of 9.1–19.5 l min ⁻¹ and a particle size range of 0.5–25 μm. Both liquid and solid particles were used. For varying the gas properties, air and argon were used.The experimental results suggest that in addition to the gas viscosity, the gas density plays an equally important role in cyclone performance. It was found that increasing the gas density enhances particle collection characteristics. Among the several parameters tested, the Reynolds number using the inlet gas velocity and the exit tube diameter was found to show the strongest correlation on the cut size.     

The Precision Associated with the Sampling Frequency of Log-Normally Distributed Air Pollutant Measurements

The frequency of air monitoring necessary to characterize an air pollutant for a given time period and area is an important problem. This paper deals with the precision of measuring an air pollutant concentration. Past research has shown that the distribution of many air pollutants can be described as log-normal. Using this result equations have been developed that predict the precision of the sample mean of the air pollutant as a function of: the frequency of sampling, the standard deviation of the logarithms of the air pollution measurements, and the level of confidence. An illustration is given to demonstrate their use. The equations are used to compare sampling plans. Tables are presented showing the precision associated with five sampling plans, for three geometric standard deviations, for three levels of confidence, and five periods of time over which the sampling plan is employed.

In an Appendix a mathematical development is presented showing the theoretical derivation of the equations. With these equations the precision of a sampling plan can be determined for any level of confidence or period of time. All that is needed is an estimate of the geometric standard deviation for the air pollution measurements.

Finally, the theoretical model is applied to air monitoring data that were collected at Roselawn School in Cincinnati, Ohio, between January 3, 1968, and April 1, 1968. The 90-day period was divided into three 30-day periods. All possible samples of size three were taken from each of the 30-day periods and their means and confidence intervals were calculated. The number of times the confidence intervals contained the true means was determined. The actual number of samples accepted as having contained the true mean, for the 80, 90, 95, and 9 9% level of confidence compared favorably with the theoretical. It is concluded that the model adequately described the behavior of air pollutants.     

ESP粉尘收集性能的影响因素

为了进一步提高电除尘器的收尘效率,尤其是对高比电阻粉尘的收尘效率,依据非稳态静电收集理论,对影响电除尘器粉尘收集性能各项因素的作用程度及机理进行了进一步研究。实验研究了粉尘收尘效率与不同比电阻粉尘的最优极间距、最优工作电压、粉尘层厚度和比电阻之间的相互关系。研究结果表明,随着极间距的增加,对应比收尘极面积,对于不同比电阻粉尘的收尘效率的增加幅度是不同的,其中高比电阻粉尘的收尘效率增加的趋势更加显著;粉尘比电阻越高,所对应的最优极间距越大,宽间距电除尘器对捕集高比电阻粉尘具有一定优越性;在最优极间距条件下,粉尘比电阻越高,其所对应的最优工作电压越小;相对于正常比电阻粉尘,随极板沉积粉尘层厚度的增加,高比电阻粉尘的最佳收尘效率所对应的最优工作电压升高幅度较大,而且最优工作电压所对应的收尘效率下降显著。随粉尘比电阻的增大,电除尘器收尘效率逐渐降低,特别是当粉尘比电阻大于1011Ω.cm后,粉尘收尘效率显著下降。研究结果与非稳态静电收尘理论提出的观点相吻合,有助于透彻理解电场结构和运行参数与粉尘收集性能的关系,特别是对于今后研发提高高比电阻粉尘收集性能的针对性技术措施具有指导作用。     

The Efficiency of Electrostatic Precipitators Under Conditions of Corona Quenching

The suppression of corona by particle space-charge is of considerable importance in electrostatic precipitators dealing with medium to high concentrations of particulates. However, the effect of the dust concentration on collection efficiency has found no direct answer in the literature. In addition to the expected reduction in corona current due to low mobility dust particles, the presence of these charged particles has two other main effects: 1. The electric field in the vicinity of the discharge electrode is weakened and hence the concentration of ions originating in the ionization zone and forming the charging current is decreased. 2. The resulting space-charge build-up causes an increase in the field strength adjacent to the collecting surface of the precipitator. The importance of each of these effects on the collection efficiency will be dependent on the relative decrease in particle charge as compared to the increase in the collection field. Experiments were carried out under both positive and negative corona with aerosol concentrations having specific surfaces in the range 0 to 44 m²/m³. These results showed: 1. For low values of corona current densities, as the specific surface area increases, the efficiency decreases. In this cqse, the charge per particle decreases as the particle concentration increases and becomes far below the normal charge attainable. Here the increase in the collection field is more than counteracted by the jarge reduction in particle charge. 2. For higher values of initial corona current densities, as the particle specific surface area increases, the efficiency either increases slightly or stays constant, in spite of major reductions in the measured corona current. In this case there should also be a reduction in the charge per particle with the increase in particle concentration, however, this is apparently offset by the increase in the collection field strength. Analysis of the results, coupled with an interpretation of existing theories, indicates that a major parameter that must be considered is the ratio of the initial corona current density and the specific surface of the particles.     

Filtration of Airborne Particulates by Gravel Filters: I. Initial Collection Efficiency of a Gravel Layer

An equation derived for initial collection of efficiency E₀ of a gravel bed filter predicts that — ln(1 — E₀) is proportional to the thickness of the gravel layer, to the — 5/3 power of the diameter of uniform gravels, and to the — 2/3 power of the Darcy airflow velocity. The experimental data obtained from NH₄CI fume removal from dry air at room temperature by sieved gravel fractions generally supported the equation, except that the effect of mean gravel size was represented by the —1.43 power of the average diameter.     

Physical characterization of the fine particle emissions from commercial aircraft engines during the Aircraft Particle Emissions eXperiment (APEX) 1–3

The fine particulate matter (PM) emissions from nine commercial aircraft engine models were determined by plume sampling during the three field campaigns of the Aircraft Particle Emissions Experiment (APEX). Ground-based measurements were made primarily at 30 m behind the engine for PM mass and number concentration, particle size distribution, and total volatile matter using both time-integrated and continuous sampling techniques. The experimental results showed a PM mass emission index (EI) ranging from 10 to 550 mg kg^?1 fuel depending on engine type and test parameters as well as a characteristic U-shaped curve of the mass EI with increasing fuel flow for the turbofan engines tested. Also, the Teflon filter sampling indicated that ～40–80% of the total PM mass on a test-average basis was comprised of volatile matter (sulfur and organics) for most engines sampled. The number EIs, on the other hand, varied from ～10¹⁵ to 10¹⁷ particles kg^?1 fuel with the turbofan engines exhibiting a logarithmic decay with increasing fuel flow. Finally, the particle size distributions of the emissions exhibited a single primary mode that were lognormally distributed with a minor accumulation mode also observed at higher powers for all engines tested. The geometric (number) mean particle diameter ranged from 9.4 to 37 nm and the geometric standard deviation ranged from 1.3 to 2.3 depending on engine type, fuel flow, and test conditions.