Calculating Collection Efficiencies for Electrostatic Precipitators

The body of information presented In this paper is directed to those Individuals involved In research on, or the design of, electrostatic precipitators. A model for calculating collection efficiencies— one based solely on physical principles and, as a result, one requiring no prior Information from pilot plant or field testing—has been employed to generate performance curves for twelve Industries presently using electrostatic precipitators. These industries Include the electric power, cement, pulp and paper, steel, chemical, and petroleum industries. The performance curves describe the predicted collection efficiency as a function of preclpltator length, plate-to-plate spacing and average field strength, and are presented In graphical, tabular, and equation form. Wherever literature values for a particular Industry are available, comparisons are made between the collection efficiencies generated by the new model and those based on actual preclpltator performance. The two are generally found to be In reasonable agreement.

The use of the Deufsch-Anderson model for preclpltator design Is also discussed. Results from the new model demonstrate that collection efficiency Is sensitive to particle size distribution, a complication that cannot be easily treated In the Deutsch-Ander-son equation which, In Its unmodified form, requires the use of a single representative particle size. It is concluded that the new model Is potentially a more realistic and viable approach to the prediction of collection efficiencies and as such should prove to be a valuable aid in electrostatic preclpltator design.     

An Aerosol Sampler for Determination of Particle Concentration as a Function of Size and Time

A high flow rate four-stage impacfor was developed for the determination of aerosol concentration as a function of both particle size and time. The unit is very useful for long-term sampling intervals (24 hr) and for sampling very dusty atmospheres. Gas-borne particulate matter is collected out on four rotating drums, each with a collection surface area of about 10 sq in.; this allows a large quantity of materials to be collected without danger of particle build-up and blow-off. A particle size-collection efficiency calibration for the unit is presented together with experimental data on wall losses, surface coatings, and other important operational considerations.     

Prediction of particulate loading in exhaust from fabric filter baghouses with one or more failed bags

Loss of filtration efficiency in a fabric filter baghouse is typically caused by bag failure, in one form or another. The degree of such failure can be as minor as a pinhole leak or as major as a fully involved baghouse fire. In some cases, local air pollution regulations or federal hazardous waste laws may require estimation of the total quantity of particulate matter released to the environment as a result of such failures. In this paper, a technique is presented for computing the dust loading in the baghouse exhaust when one or more bags have failed. The algorithm developed is shown to be an improvement over a previously published result, which requires empirical knowledge of the variation in baghouse pressure differential with bag failures. An example calculation is presented for a baghouse equipped with 200 bags. The prediction shows that a small percentage of failed bags can cause a relatively large proportion of the gas flow to bypass the active bags, which, in turn, leads to high outlet dust loading and low overall collection efficiency from the baghouse.     

Prediction of Particulate Loading in Exhaust from Fabric Filter Baghouses with One or More Failed Bags

Abstract

Loss of filtration efficiency in a fabric filter baghouse is typically caused by bag failure, in one form or another. The degree of such failure can be as minor as a pinhole leak or as major as a fully involved baghouse fire. In some cases, local air pollution regulations or federal hazardous waste laws may require estimation of the total quantity of particulate matter released to the environment as a result of such failures. In this paper, a technique is presented for computing the dust loading in the baghouse exhaust when one or more bags have failed. The algorithm developed is shown to be an improvement over a previously published result, which requires empirical knowledge of the variation in baghouse pressure differential with bag failures. An example calculation is presented for a bag-house equipped with 200 bags. The prediction shows that a small percentage of failed bags can cause a relatively large proportion of the gas flow to bypass the active bags, which, in turn, leads to high outlet dust loading and low overall collection efficiency from the baghouse.     

The Prediction of Overall Collection Efficiency of Air Pollution Control Devices from Fractional Efficiency Curves

The application of air pollution control devices requires the prediction of overall collection efficiency from the particle size distribution of the dust and the fractional efficiency of the air pollution control device. The cumulative particle size distribution of dust resulting from industrial processes can usually be represented by a straight line on logarithmic probability paper or a log normal function. The fractional efficiency curves of many air pollution control devices such as cyclones or wet scrubbers can also be adequately represented by a log normal function. Only two parameters are required to define a log normal function, a median diameter and a geometric standard deviation. Both of these can easily be obtained from a plot on logarithmic probability paper. The overall collection efficiency has been found to be Very simply related to the four parameters required to define the log normal functions representing the particle size distribution and the collector fractional efficiency. These four parameters are: the mass median diameter and the geometric standard deviation of the dust size distribution, the cut diameter (50% efficiency diameter), and geometric standard deviation of collector fractional efficiency curve. Using this relationship the prediction of overall collection efficiency is greatly simplified with no loss of accuracy.     

The availability and fall-out of an insecticidal aerosol dispersed from aircraft during operations for control of tsetse fly in Zimbabwe

Droplet availability (numbers and volume crossing unit vertical area) has been measured by means of rotary slide samplers and the measurements have been converted to estimates of the most likely dose received by a tsetse fly using collection efficiency data for samplers and flies derived from laboratory wind tunnel study. The resulting dosage levels indicate high probability of effective fly control, except that in the centre of the block the parting effect of change of wind direction between sorties which occurred during the first two cycles of application has left a narrow band uncovered by spray. Deposition to the ground at points within the block and up to 4 km beyond the downwind margin has been measured to provide data for correlation with environmental effects to be observed by an independent biological study team.     

The Effective Collection of Fly Ash At Pulverized Coal-Fired Plants

The relationship between sulfur in coal, boiler exit gas temperature, and the carbon portion of fly ash have a major effect on the electrical properties of fly ash. Whether effective collection of fly ash is obtained by the electrostatic precipitator installation alone or the precipitator—mechanical combination depends primarily on a knowledge of this relationship. Fly ash electrical properties can range from a highly "resistive" to a highly "conductive" state which can appreciably alter the precipitator collection performance. A correlation of coal sulfur and boiler exit flue gas temperature is given to indicate the probability of expecting an optimum voltage—current relationship with different combinations of these factors. Carbon affects the electrical conditioning of fly ash by providing parallel paths of current leakage through the deposited dust layer. Therefore, removal of the carbon particles in a mechanical collector placed before the precipitator can alter the precipitator electrical characteristics.     

Fuel consumption, emissions estimation, and emissions cost estimates using global positioning data

The methodology laid out in this paper shows that typical operational data from vehicle fleets monitored by a global positioning system (GPS) can be used to estimate heavy-duty diesel vehicle (HDDV) emissions, thereby enabling waste managers and governing bodies to internalize the responsibility for socioenvironmental costs traditionally absorbed by external parties. Although municipal solid waste (MSW) collection vehicles are the subjects of this particular study, the methodology presented here can be applied to any fleet of vehicles monitored by GPS. This study indicates that MSW collection trucks may be considerably less fuel efficient in the field than published values for HDDV fuel efficiency suggest. The average fuel efficiency of one MSW collection truck was estimated as 0.90 +/- 0.44 km/L (2.12 +/- 1.03 mi/gal). This same truck would generate approximately 42 metric tons of CO2 equivalents/yr, which is comparable to the greenhouse gas emissions of a large sport utility vehicle driving six times the distance, in town, for a year. In terms of the impacts such emissions have, projections for the monetary cost of emissions are available but highly variable. They suggest that the external monetary costs of emissions range between 6 and 39% of the annual fuel costs for the studied MSW collection truck. The results of this study indicate a need for further research into valuation of the hidden, external costs of emissions, borne by local and global socioecological communities. The possible implications of this result include poorly advised fleet procurement decisions and underestimation of MSW collection fleet emissions.     

Collection efficiency of a midget impinger for nanoparticles in the range of 3–100 nm

Impingers have been employed for collection of biological particles for a long time and the collection efficiency for submicron particles has been well studied for a few impinger models, like the SKC Biosampler and the AGI 30. These efficiency studies have been limited to particles larger than about 15 nm. The aim of this research is to determine the collection efficiency of ultrafine particles (from 3 to 100 nm) of a 25 ml midget impinger. The effect of different collection parameters (particle type, collection fluid volume and type and flow rate) was studied and results are presented here. All results showed minimum collection efficiencies from 3 to 10% at approximately 40–57 nm. Increasing the volume of the collection liquid and flow rate improved the collection efficiency of the impinger.     

Pollution control by reduction of drag on cars and buses through platooning

Platooning is synchronised movement of two or more vehicles, as a unit, travelling at the same speed with relatively small inter-vehicle spacing. It is generally done in order to increase the highway capacity (vehicles/lane/hour). It was recognised early on that close follow up would likely decrease the average vehicle drag. The authors also expected minimisation of drag on cars and buses moving in platoons. Therefore, estimation of drag on a maximum four-vehicle platoon model was carried out inside Jadavpur University Subsonic Low Turbulence Closed Circuit Wind Tunnel test section. Several car models and bus models were used as platoon members in this experiment. The results show significant drag minimisation, which in turn decreases fuel consumption. Less fuel consumption indicates less air pollution, which is the talk of the day in large cities.     

Closing Remarks

Abstract

The recent standards of performance for wastewater sources in the Synthetic Organic Chemical Manufacturing Industry (SOCMI), published by the U.S. Environmental Protection Agency (EPA), call for treatment of waste–water containing 500 ppmw volatile organic compounds (VOCs) and operating at flow rates greater than 1.0 liter per minute. There are a number of methods for achieving compliance with the treatment standards for wastewater. Among these is treatment to a VOC concentration of less than 50 ppmw with the removal of total VOC mass from the wastewater stream by 95%. If the wastewater treatment system uses stripping or evaporation, then the unit must be covered and vented to a control device. Emissions from the vent control system must be no greater than 20 ppmw. In this work, a treatment system is designed that would achieve compliance with the published standards. A novel unit operation—thin–film evaporation into a natural gas receiving stream—is used to treat the wastewater stream, while the vapor stream is combusted in a boiler or similar fired unit. The process employs a multimedia approach to minimize total treatment costs.     

Electrostatic Precipitation of Ultrafine Particles Enhanced by Simultaneous Diffusional Deposition on Wire Screens

Abstract

A laboratory-scale electrostatic precipitator has been designed and constructed in which the grounded collector plate has been substituted by a set of wire screens placed perpendicularly to the gas flow. Particles are deposited onto the screens by two mechanisms—electrostatic deposition and diffusional deposition—which act simultaneously. On the one hand, electrostatic deposition is effective for relatively large particles, but it is quite ineffective for the smallest ones because their charging probability in the corona field is too low. On the other hand, the diffusional collection efficiency of particles on fibers is high for small particles but low for the larger ones. Therefore, the simultaneous diffusional-electrostatic precipitation may become a useful technique for efficient filtration of particles below 0.1 μm. A preliminary experimental evaluation of this filtering device has shown that submicrometer particles with diameters down to a few nanometers can be collected with number efficiencies greater than 99%.     

Shortest service location model for planning waste pickup locations

A municipal solid waste (MSW) and recycled material curbside pickup bus system was recently initiated in a Taiwan city to improve collection service. For such an MSW pickup system, selecting appropriate collection stops critically affects hauling costs and service efficiency. Conventionally, MSW collection points are heuristically and manually chosen, resulting in a hauling system that is not as effective as intended in terms of location suitability and the number of collection points. The Shortest Service Location (SSL) model, which minimizes the sum of service distances, was therefore proposed in this study. The SSL model was compared with two other models for a local MSW pickup system problem. Using georeferenced graphs generated by a geographical information system (GIS) and related programs, the performance of the three models was compared according to walking distance to a service stop, the coverage of a service stop, and the number of service stops. The results show that the SSL solution can shorten walking distances by approximately 10% and reduce the overlap of service areas covered.     

Moss bags as sentinels for human safety in mercury-polluted groundwaters

An equation to estimate Hg concentrations of <4 μg/L in groundwaters of a polluted area in NE Italy was set out by using transplants of the aquatic moss Rhynchostegium riparioides as trace element bioaccumulators. The equation is derived from a previous mathematical model which was implemented under laboratory conditions. The work aimed at (1) checking the compliance of the uptake kinetics with the model, (2) improving/adapting the model for groundwater monitoring, (3) comparing the performances of two populations of moss collected from different sites, and (4) assessing the environmental impact of Hg contamination on a small river. The main factors affecting Hg uptake in the field were—as expected—water concentration and time of exposure, even though the uptake kinetics in the field were slightly different from those which were previously observed in the lab, since the redox environmental conditions influence the solubility of cationic Fe, which is a negative competitor of Hg²⁺. The equation was improved by including the variable ‘dissolved oxygen concentration’. A numerical parameter depending on the moss collection site was also provided, since the differences in uptake efficiency were observed between the two populations tested. Predicted Hg concentrations well fitted the values measured in situ (approximately ±50 %), while a notable underestimation was observed when the equation was used to predict Hg concentration in a neighbouring river (?96 %), probably due to the organic pollution which hampers metal uptake by mosses.     

Thermodynamic analysis of in situ gasification-chemical looping combustion (<Emphasis Type="Italic">i</Emphasis>G-CLC) of Indian coal

Chemical looping combustion (CLC) is an inherent CO₂ capture technology. It is gaining much interest in recent years mainly because of its potential in addressing climate change problems associated with CO₂ emissions from power plants. A typical chemical looping combustion unit consists of two reactors—fuel reactor, where oxidation of fuel occurs with the help of oxygen available in the form of metal oxides and, air reactor, where the reduced metal oxides are regenerated by the inflow of air. These oxides are then sent back to the fuel reactor and the cycle continues. The product gas from the fuel reactor contains a concentrated stream of CO₂ which can be readily stored in various forms or used for any other applications. This unique feature of inherent CO₂ capture makes the technology more promising to combat the global climate changes. Various types of CLC units have been discussed in literature depending on the type of fuel burnt. For solid fuel combustion three main varieties of CLC units exist namely: syngas CLC, in situ gasification-CLC (iG-CLC) and chemical looping with oxygen uncoupling (CLOU). In this paper, theoretical studies on the iG-CLC unit burning Indian coal are presented. Gibbs free energy minimization technique is employed to determine the composition of flue gas and oxygen carrier of an iG-CLC unit using Fe₂O₃, CuO, and mixed carrier—Fe₂O₃ and CuO as oxygen carriers. The effect of temperature, suitability of oxygen carriers, and oxygen carrier circulation rate on the performance of a CLC unit for Indian coal are studied and presented. These results are analyzed in order to foresee the operating conditions at which economic and smooth operation of the unit is expected.     

The effects of thermophoresis and diffusiophoresis on the collection of charged sub-μm particles by charged droplets

The collection efficiency of charged water droplets of 500 μm diameter for charged particles of 0.2 μm diameter is examined as a function of the nondimensional Coulombic parameter. The present paper provides an experimental technique to determine the contribution of the phoretic forces in particle collection by comparing the collection efficiencies of water droplets to that of oil droplets for which the vapor pressure and the phoretic forces are negligible. Reasonable agreement is obtained between the experimental data and the values predicted by a collection efficiency model considering only Coulombic force, thermophoresis and diffusiophoresis.     

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.     

Evaluation of Saltzman and Phenoldisulfonic Acid Methods for Determining NOx in Engine Exhaust Gases

The two methods normally used for the analysis of NO_x are the Saltzman and the phenoldisulfonic acid technique. This paper describes an evaluation of these wet chemical methods to determine their practical application to engine exhaust gas analysis. Parameters considered for the Saltzman method included bubbler collection efficiency, NO to NO₂ conversion efficiency, masking effect of other contaminants usually present in exhaust gases and the time-temperature effect of these contaminants on stored developed solutions. Collection efficiency and the effects of contaminants were also considered for the phenoldisulfonic acid method. Test results indicated satisfactory collection and conversion efficiencies for the Saltzman method, but contaminants seriously affected the measurement accuracy particularly if the developed solution was stored for a number of hours at room temperature before analysis. Storage at 32°F minimized effect. The standard procedure for the phenoldisulfonic acid method gave good results, but the process was found to be too time consuming for routine analysis and measured only total NO_x.     

Precipitation of Charged Dust Particles on Electrostatic Screen

The purpose of this paper is to present collection performance dependence upon the parameters of channeled electrodes in a twostage precipitator. The practical channeled electrostatic screens are classified into two types and the respective theoretical collection efficiency equations are obtained by employing idealized models. It is shown that In normal operating conditions the most effective particle collection mechanism in the device is electrostatic precipitation rather than the Inertlal separation. It is also pointed out that the channeled electrode, in comparison with the plate-type, should be a narrow width. An empirical efficiency equation is recommended and the agreement between experimental data and empirical equation is within 6%.     

State Standards,Regulations, and Responsibilities in Noise Pollution Control

In the near future the State of Minnesota will adopt noise pollution standards and regulations based on the findings presented in this paper. Comprehensive noise standards are presented for all sources of noise, including airports, highways, and industrial sources. Two of the three dimensions of noise—intensity and frequency—are measured by the use of the unit dBA, whereas the third dimension—duration—is measured by use of the temporal distribution, expressed as L_x, where x is the sound pressure level in dBA exceeded x% of the time. Standards are established for five zones: 1. residential—single family, 2. residential— apartments, public buildings, 3. commercial, 4. manufacturing, and 5 industrial. The L_x standards apply to most noises including industrial and highway noises. Aircraft noise and impulse noise standards are also discussed. The six phase implementation plan for noise abatement is discussed.