Electrostatic precipitator emission and opacity performance control through rapper strategy

The opacity and emission performance of two “identical” cold-side precipitators at a power plant utilizing a Western coal source was investigated through an extensive test program. The test program included establishment of outlet emission versus opacity correlations for the two “identical” units, correlation of rapper strategy (frequency and amplitude) with opacity, and correlation of power-off rapping strategy with opacity. Analysis of the test program data demonstrates that the opacity-emission correlations from the two “identical” units can be significantly different. The potential reasons for the differences between the two units are identified and examined in light of the test program data. Strong correlation of opacity with rapping strategy was developed from the test program. Results demonstrate that an automatic power-off rapping technique can significantly enhance precipitator performance on ash from Western coal.     

The effects of corona electrode geometry on the operational characteristics of an ESP

Experiments were run in a pilot scale electrostatic precipitator (ESP) to determine the effects of corona wire-to-wire spacing on the operating conditions. Tests were run, using a reentrained low sulfur fly ash at both hot- and cold-side conditions. The effects of varying wire-to-wire spacing were determined. Results are given which show that varying wire spacing at cold-side conditions has little operational effect on the ESP while improved efficiency can be obtained at hot-side (low resistivity) conditions by reducing wire spacing. The increased efficiency results from a higher average operating voltage. The effects of back ionization are clearly demonstrated by a set of experiments in which dust was selectively removed from the wires or plate. These tests show that the lower operating voltage caused by back ionization is a combined effect of high resistivity dust on both the wires and plate.     

Precipitator upgrading and fuel control program for particulate compliance at Pennsylvania power and light company

Two cold side electrostatic precipitators handling low sulfur eastern bituminous coal flyash were upgraded from 94% to 99.4% efficiency in order to meet a particulate compliance limit of 0.1 lb/MMBtu (43 ng/J).The comprehensive upgrading was the result of a 2 year research and testing program during which various aspects of flue gas conditioning, electrical energization, rapping, coal quality control, and gas distribution were independently tested on three similar precipitators. The ensuing upgrading program included the installation of hardware for maximum performance and reliability as well as flue gas conditioning and a fuel ash control program.A cost and reliability analysis of the upgrading program as compared with the installation of an additional series precipitator is included.     

Size dependent cytotoxicity of fly ash particles

Fly ash samples were collected from the electrostatic precipitator of a coal-fired power plant in Hong Kong. The particles of the respirable range (smaller than 10 μm) were divided into 4 groups according to their particle size (mass median aerodynamic diameters). The surface morphology and the metal contents (Fe, Mn, Al and Zn) of fly ash particles were examined by a scanning electron microscope and an inductively coupled plasma spectrophotometer, respectively. The particles were very heterogenous in size and shape as well as the concentration of metals. The cytotoxicity of these four groups of fly ash particles was evaluated using an in vitro rat alveolar macrophages culture assay. The viability of alveolar macrophages was lower when incubated with smaller size particles. This relationship was also reflected by the damage of the surface morphology of the cells and the release of cytoplasmic (lactate dehydrogenase) and lysosomal (acid phosphatase and β-glucuronidase) marker enzymes into the culture media.     

Precipitator energization utilizing an energy conserving pulse generator

The performance of a conventional two-electrode type precipitator collecting high resistivity dust can be improved by pulse energization. Pulses of a suitable duration and repetition rate superimposed on the DC voltage permit higher peak-voltage without sparkover, improve particle charging and current distribution, and allow independent regulation of the precipitator voltage and current. A considerable quantity of energy, however, is required for each pulse to charge the precipitator to the pulse voltage level. For high pulse voltages only a minor part of this energy is necessary for the discharge current in the precipitator. For reasons of economy, the recovery of the energy stored in the precipitator capacitance during each pulse is therefore extremely important for pulse energization of large precipitators. An energy conserving pulse generator with pulse transformer, a pulse initiating switch element, and a feed-back diode for the energy recovery is described. The design and the instrumentation of a pilot precipitator specially developed for the comparison of different kinds of precipitator energization are outlined. The ability of the applied pulse energization system for controlling the corona discharge current independently of the precipitator voltage is demonstrated. Further, results from field tests showing the performance of the system under operating conditions are presented.     

Control of fine particle emissions with wet electrostatic precipitation

This paper presents the results, both pilot and full-scale, of experience with the application of wet electrostatic precipitation technology for the control of fine particle emissions from industrial processes. Performance data involving the collection of such difficult-to-clean emissions as a sulfuric acid mist and recovery boiler salt fume are presented. The measured wet precipitator performance parameters (e.g., SCA, effective migration velocity) are compared to those reported in literature for dry precipitators operating on equivalent processes. Particular emphasis is directed toward examining wet electrostatic precipitator performance levels in controlling very high concentrations of submicron fume with the accompanying problem of space charge corona quenching. Relationships between these performance data and specific wet precipitator operating parameters such as operating voltage and current density are also examined.     

Partitioning coefficients of polycyclic aromatic hydrocarbons in stack gas from a municipal incinerator

In this study, solid-gas partitioning coefficients of PAHs on fly ash in stack gas from a municipal incinerator were determined according to elution analysis with gas-solid chromatography. The fly ash from the electrostatic precipitator was sieved and packed into a 1/4 inch (6.3 mm) pyrex column. Elution analysis with gas-solid chromatography was conducted for three PAHs, Napthalene, Anthracene, and Pyrene. The temperature for elution analysis was in the range of 100°C to 300°C. V_g, specific retention volume obtained from elution analysis, and S, specific surface area of fly ash measured by a surface area measurement instrument, were used to estimate the solid-gas partitioning coefficient, K_R. In addition, the relationships between K_R and temperature and K_R and PAH concentrations were investigated.     

Theoretical methods for computing electrical conditions in wire-plate electrostatic precipitators

A new semi-empirical, approximate theory for predicting electrical conditions is described. In the approximate theory, analytical expressions are derived for calculating voltage-current characteristics and electric potential, electric field, and space charge density distributions. Comparisons of numerical and approximate solutions over a wide range of possible precipitator geometries and electrical operating points indicates that for practical purposes the approximate theory can be used in lieu of the more rigorous numerical theory. This saves large amounts of computer time and makes possible hand calculator usage. Recent in situ gaseous ion mobility data which are needed in the models are presented. For coal fired power plants, the reduced effective ion mobility in positive corona is found to be 1.6 times that for negative corona. Approaches for describing particulate space charge effects in the gas and electrical conditions in the collected particulate layer are briefly discussed.     

Electrode cleaning systems: Optimizing rapping energy and rapping control

Methods for improving electrostatic precipitator performance by increasing electrode excitation level during rapping, and by optimizing rapping control, are presented in this paper. Design modifications can reduce mechanical impedence to vibration transmission during rapping. These same modifications can eliminate areas of high stress concentration where fatigue failure often occurs. Rapping system control parameters are presented as they relate to variations in field collection and shedding rates. Anti-coincident rapping control for plate rappers minimizes peak opacity levels during rapping if sufficient “rest times” between raps can be maintained. When anti-coincidence must be sacrificed due to insufficient rest times on large installations, suggestions for anti-coincident rapping by section are presented. Methods for optimizing field rapping repeat rates using available opacity, ash pull, and precipitator power information are discussed.     

Trace and major element pollution originating from coal ash suspension and transport processes

Coal ash obtained by coal combustion in the "Nikola Tesla A" power plant in Obrenovac, near Belgrade, Yugoslavia, is mixed with water of the Sava river and transported to the dump. In order to assess pollution caused by leaching of some minor and major elements during ash transport through the pipeline, two sets of samples (six samples each) were subjected to a modified sequential extraction. The first set consisted of coal ash samples taken immediately after combustion, while the second set was obtained by extraction with river water, imitating the processes that occur in the pipeline. Samples were extracted consecutively with distilled water and a 1 M solution of KCl, pH 7, and the differences in extractability were compared in order to predict potential pollution. Considering concentrations of seven trace elements as well as five major elements in extracts from a total of 12 samples, it can be concluded that lead and cadmium do not present an environmental threat during and immediately after ash transport to the dump. Portions of zinc, nickel and chromium are released during the ash transport, and arsenic and manganese are released continuously. Copper and iron do not present an environmental threat due to element leaching during and immediately after the coal ash suspension and transport. On the contrary, these elements, as well as chromium, become concentrated during coal ash transport. Adsorbed portions of calcium, magnesium and potassium are also leached during coal ash transport.     

本钢发电厂粉煤灰综合利用途径和方案的探讨

本钢发电厂的粉煤灰是本溪环境污染源之一,同时粉煤灰又是一种资源。该厂建厂50余年,先后建成15台锅炉,经环保治理后灰渣年排放约50万t。由于锅炉型号、煤种、温度、排灰方式等不同,灰的物理、化学性质、粒度等也不同:而不同的粉煤灰制品对粉煤灰的技术指标要求也不同;因此,本文对该厂的粉煤灰按不同的炉子,不同的性质,研制出不同的利用途径,以及探讨制定出鼓励和扶植对粉煤灰综合利用的相应政策和措施。     

Radiological impact of coal-fired power generation

A radiological impact assessment was carried out at the 4000 MW Nanticoke Thermal Generating Station on the north shore of Lake Erie and at an ash disposal site in Metropolitan Toronto, both operated by Ontario Hydro. Analyses were performed on feed coal, fly ash and bottom ash and on samples of air filters, precipitation, water, soil and vegetation in the vicinity of the generating station. The measured radionuclide levels in the vicinity of the generating station showed no evidence of enhancement from station emissions. There were no indications that leaching of radionuclides or emanation of radon gas from ash disposal sites would be a problem. There was evidence, however, of higher radionuclide concentrations on the finer ash particles. Furthermore, the use of fly ash in building materials could lead to enhanced radiation levels. Atmospheric dispersion and radiation dose calculations were also carried out. Predicted concentrations in air were all less than 1% of background values. The committed dose equivalent from one year of operation was estimated to be 0·27 μSv at the site boundary and 0·11 μSv at 10 km east of the site.     

Ion current densities produced by energetic electrons in electrostatic precipitator geometries

A new laboratory test system for electron beam ionization in electrostatic precipitator geometries has been constructed to measure ion current density as a function of voltage difference for clean plate (no dust contamination) conditions. The new system incorporates improved electrodes which withstand an applied voltage of ± 55 kV, a factor of 5 increase over the previous test system. A 3 MeV Van de Graaff accelerator produced ionizing electron beams of 1.2 and 2 MeV energy with beam currents of 10.5 and 21 μA in place of corona wire ionization. Ion current densities of up to 130 mA/m² were measured before breakdown between the plates, and no ion current saturation was observed. A comparison of I-V curves and sparkover voltages for various beam energies, currents, and types of collimation is discussed and the need for measurements with good beam geometry is addressed.     

Polychlorinated biphenyls in ambient air of NW Greece and in particulate emissions

Polychlorinated biphenyls (PCBs) bound to total suspended particles (TSP) were determined in the area of Eordea basin, NW Greece, where intensive coal burning for electricity production takes place. The concentrations of PCBs exhibited high variability although within the range reported for urban industrialized areas. The presence of PCBs in fly ash generated from coal burning as well as in particulate emissions from vehicles, domestic heating, burning of refuses and biomass was also examined. The particles emitted from vehicles and central heating exhibited the higher content of PCBs, whereas fly ash the lower. The pattern of PCBs in TSP as well as in particulate emissions was discussed.     

Interaction between electrostatics and fluid dynamics in electrostatic precipitators

Significant effort has been devoted by past researchers in electrostatic precipitators to electrostatics and particle chemistry. Relatively little, however, has been published on the effect of turbulent flow and its interaction with electrostatics and particle dynamics. This paper describes an experiment and a fundamental model which is focused on the coupled effects of the fluid dynamics and electrostatics.A laboratory precipitator flow facility with laser beam illumination was used to visualize smoke flow. Detailed photographs of flow patterns with and without electric field were recorded in a horizontal plane through the precipitator.A theoretical model was used to numerically simulate the observed flow patterns in the experiment. In the model the flow was described by time-averaged mass and momentum equations with a two-equation turbulence model. The electric field was described by Maxwell electrostatic equation and the continuity of the current equation. The system of the coupled partial differential equations was solved by a finite difference scheme.The interaction between fluid dynamics and electrostatics is shown to have a significant role in altering the flow in the precipitator. The practical implication is that the interaction will aid in particle migration in some regions, but it will increase reentrainment and reduce particle migration in others. Comparison between the results from the experiment and numerical computations shows good qualitative agreement between the two. Since both the electrostatic and the fluid dynamic flow fields depend on the electrode geometry, further investigation may lead to improved design of precipitators.     

Disequilibrium between uranium and its progeny in the Lake Issyk-Kul system (Kyrgyzstan) under a combined effect of natural and manmade processes

The Kadji-Sai abandoned field of U-bearing brown coal on the southern coast of Lake Issyk-Kul (Kyrgyzstan) poses a threat of radioactive pollution to the world's fifth deepest and second largest pristine highland lake. The valleys of ephemeral streams in the lake catchment are filled with coarse-grained sand and clay, with a background U--Ra activity of 35--55 Bqkg(-1). High activity areas vs. this background come from three sources: (1) scarce outcrops of uraniferous brown coal and mining wastes containing fragments of this coal with (238)U/(226)Ra ratios of 0.8 due to uranium losses through weathering; (2) manmade anomalies caused by a radioactive waste dump, where U was extracted from the ash of coal burnt at a coal-fired power plant. As a result, the (238)U/(226)Ra ratios become 0.15--0.25; (3) six catch pools terraced below the mine, where U activity decreases downslope, and (238)U/(226)Ra ratios reach 150--200. Uranium lost in the extraction process may have been retained on the terraces. The distribution pattern of radionuclides in the bottom sediments of the lake is controlled by water depth and offshore distance. The upper section of homogeneous limy--argillic deposits in the lake center remains undisturbed by currents, as indicated by regular sub-exponential distribution of atmospheric (137)Cs and (210)Pb(atm). Sedimentation rate in the lake center for the past century, found from (210)Pb, was 0.32 mmyr(-1). (238)U/(226)Ra in deep-water sediments was about 3. The activity of uranium adsorbed by sediments from the lake water was estimated by subtraction of the Ra-equilibrium component from the total U activity. Thus, the flux of dissolved U to the bottom sediments was as 2.07 x 10(-7)gcm(-2)yr(-1). The upper section of near-shore deposits was disturbed by currents, with (137)Cs and (210)Pb(atm) more or less uniformly distributed in this layer. Peaks of (226)Ra and (210)Pb occur at different depths from 5 to 20 cm below the sediment surface, with (238)U/(226)Ra ratios 0.28--0.44. The presence of mullite in these sediments indicated that radioactive ash penetrated into the lake in the past. At present, (226)Ra in the ash is buried under a non-radioactive cap.     

Chemical speciation and phytoavailability of Zn, Cu, Ni and Cd in soil amended with fly ash-stabilized sewage sludge

A sequential extraction method was used to determine chemical forms of Cu, Zn, Ni and Cd in fly ash-stabilized sludge. A loamy acid soil amended with fly ash-stabilized sludge was used to grow corn under greenhouse conditions. Sewage sludge amended with coal fly ash can reduce the availability of Cu, Zn, Ni and Cd in the sludge. Increasing fly ash amendment rate significantly reduced DTPA-extractable Cu, Zn, Ni and Cd concentrations. Percentages of Cu, Zn and Ni in residual fraction increased with an increase in fly ash amendment rates. Majority of Cu was associated with organic form, but Zn and Ni were associated with Fe-Mn oxide and residual forms. Addition of ash-amended sludge to soil significantly increased dry mass of corn. With coal fly ash amendment rate increasing, concentrations of Zn and Cu in shoot tissues of corn decreased significantly, but concentrations of Cd and Ni did not change significantly. Significant correlations were found between concentrations of Cu and Zn in corn shoot and oxide and total Cu fractions, and all chemical fractions of Zn in fly ash-stabilized sludge, respectively. Hence, ash amendment significantly reduced the availability of heavy metals by chemical modification of their chemical speciation into less available forms.     

Application of slipstreamed air pollution control devices on waste-as-fuel processes

The recovery of energy from the combustion of municipal solid wastes is becoming an attractive alternative as landfill space becomes scarce and the availability of fossil fuels decreases. Particulate emissions from “waste-as-fuel” processes, however, may differ significantly in chemical and physical properties from particulate emissions produced by firing only coal. Such differences can affect the design and operation of air pollution control equipment. Presented in this paper are the results of a 2-month test program at Ames, Iowa, with a mobile electrostatic precipitator (ESP) and a mobile scrubber supplied by the U.S. Environmental Protection Agency (EPA), Industrial Environmental Research Laboratory (IERL), Research Triangle Park. PEDCo Environmental, Inc., and Acurex Corporation jointly conducted the test program to examine the effect of burning refuse-derived fuel (RDF) on particulate and heavy metal control efficiencies. The mobile ESP was used only as a primary control device, whereas the mobile scrubber was tested both upstream and downstream of the existing full-scale ESP. This paper also presents a status report on a PEDCo test program with a pilot fabric filter at Ames.     

Eco-sanitation and its benefits: an experimental demonstration program to raise awareness in central Nepal

This study focuses on awareness and an experimental demonstration about the use of human urine and wood ash as a fertilizer. This study was conducted in Chanauta, central Nepal, from November 2009 to February 2010. The villagers (N = 27) were asked about their awareness of eco-sanitation and fertilizer value of urine and ash. All the participants agreed that the use of urine and ash was a good idea. In the experimental study, the fertilizer value of urine+ash was compared with animal manure and no-fertilizer in the cultivation of radish, potato, broadleaf mustard, cauliflower, and cabbage. Different plants cultivated plots received 54–81 kgN/ha with urine+ash or manure fertilizer. The urine+ash fertilizer produced significantly (p < 0.05) higher broadleaf mustard biomass than obtained from animal manure and without fertilization. Urine+ash-fertilized plots growing radish, potato, cauliflower, and cabbage produced similar or slightly higher yields biomass compared to those achieved with manure fertilization. This might be because of high P, K as well as greater availability of N in applied urine compared to manure. It is concluded that urine+ash fertilizer can be used instead of animal manure; in this study, a dose of 4 L of urine was equal to 1 kg of dry cattle manure and produced a similar or greater yield of vegetable biomass than manure fertilization. To be able to generalize this conclusion, it is important to conduct these kinds of experiments with different seasonal crops and in other parts of the world.