Collection efficiency of electrostatic precipitators by numerical simulation

A numerical simulation code has been developed to analyze the coupled electro-aerodynamic phenomena within an electrostatic precipitator operated in both the positive and negative corona modes. The space charge and current densities, as well as the static and space charge components of the electric field, are first obtained using the known cross-sections for ionization and negative ion formation. Data includes the effects of fluid flow. The above quantities (except the static field) are then corrected in a subsequent iteration for the presence of dust particles of known size distribution, charges predominantly by the field charging mechanism. The precipitator collection efficiency is calculated from the trajectories of the charged dust particles. For theory comparison, the collection efficiencies of model precipitators were measured by light-scattering techniques using oil drops as test particles. The variation of efficiency with wire-to-wire spacing will be discussed as a case study.     

Optimization of collection efficiency by varying plate spacing within an electrostatic precipitator

Use of the Deutsch equation as an evaluation tool of electrostatic precipitators has resulted in the restriction design to a single plate spacing and has not enabled optimal use of the space charge arising from the presence of charged dust particles. Space charge is dependent on dust loading and plate spacing and also influences the electric field, hence the migration velocity and, therefore, collection efficiency. Thus a trade-off is indicated between plate spacing and collection efficiency as a function of dust loading. A first step examination of this trade-off indicates that varied spacing can be used in precipitators while maintaining high levels of efficiency and decreasing the required specific collection area by 15% to 25%.     

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.     

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.     

Condensational enlargement as a supplement to particle control technologies

An experimental study has been undertaken at the Colorado School of Mines to evaluate the feasibility of using condensational enlargement to enhance the collection efficiency of existing dust control technologies for sub-micron particulates. Although the study was begun to consider the problem of respirable dust control in the underground coal mine environment, this enhancement technique shows promise for a more general class of applications. In the experiments to be reported on, particulates are injected into a continuous flow thermal diffusion chamber and subjected to varying environmental conditions; saturation ratio (rel. humidity), temperature, and residence time were the parameters. The results show that condensation on a dust nucleus (≈0.1 micron) can bring it to a size of several microns in a sufficiently short period of time as to indicate engineering applicability of the concept.     

Evaluation of the George Neal electrostatic precipitator

The Electric Power Research Institute (EPRI) is currently supporting a major research program characterizing the performance of high efficiency electrostatic precipitators (ESP). One such effort evaluating the George Neal ESP of Iowa Public Service Company is described in this paper.Results show that under well tuned conditions the ESP overall collection efficiency was 99.7% at a specific collecting area of 745 ft²/kacfm (147 m²/m³/s) (520 MW) with associated mass concentrations of 0.025 lb/10⁶ Btu and stack opacity of 4.6%. The boiler outlet size distribution was found to be bimodal with submicron and large particle peaks at 0.2 and 5 microns diameter, respectively. Consequently, an apparent bimodal fractional efficiency curve results with efficiencies of 99.6%, 98%, and 90% measured for 20, 2 and 0.2 micron diameter particles, respectively. Rapping reentrainment losses were found to be insignificant except during episodes of high ash hopper levels resulting from a malfunctioning ash removal system, when large rapping puffs were observed. In addition, outlet emissions increased dramatically to 0.08 lb/10⁶ Btu (34 ng/J) during these periods, suggesting that an emission level more representative of daily operation lies somewhere between 0.025–0.08 lb/10⁶ Btu (10.8–34 ng/J).     

Experimental investigation of dust pollutants and the impact of environmental parameters on PV performance: an experimental study

The accumulation of dust pollution on the photovoltaic (PV) module can have a significant effect on the productivity and efficiency of PV systems in different locations in the world. Dust which accumulated over time on the PV module and is based on weather conditions led to the reduction in the effectiveness of solar cells. The aim of this research was to experimentally investigate the effect of the natural dust and the effects of environmental parameters on PV performance. The experiments were conducted to propose a model for the current, voltage, power and efficiency and to simulate the effect of environmental parameters on PV performance. The natural dust investigated consisted of different compounds: SiO₂ (45.53 %), CaO (24.62 %), Al₂O₃ (10.83 %), Fe₂O₃ (10.46 %), MgO (6.33 %), K₂O (0.87 %), TiO₂ (0.45 %), SO₃ (0.24 %), MnO₂ (0.21), Cr₂O₃ (0.23 %), SrO (0.13 %) and NiO (0.09 %). It was found that the most accurate correlation is a polynomial from seventh degree for current, voltage, power and efficiency, fourth degree for solar radiation and temperature, cubic degree for humidity and wind velocity. The coefficients of general model are 0.6343, 0.0110, 0.0 and 0.0001 for PV module, respectively, with 0.0011 fitting factor. The proposed model has been validated using models in the literature.     

Pressure drop in electrostatic fabric filtration

Fabric filtration systems have been employed in industry for over a century with relatively few technological modifications. However, with the recent substantial increase in energy costs, conservation in energy consumption has become vitally important. As a result, the filtration systems of yesteryear may not be the best approach for future applications. Recently, an external electrical field was considered in fabric filtration of industrial dust with very promising initial results. An increase in the collection efficiency, particularly for fine particulates, and a decrease in the pressure drop was observed. In this paper the further results of an experimental program in the investigation of pressure drop in the electrostatic fabric filtration in industrial dust control are presented. The basic apparatus, a bench-scale electrostatic fabric filtration system, creates a representative dust cake under specific conditions of operating parameters and charge levels. The results clearly indicate that filter and dust cake resistance, or pressure drop, decreases substantially with the increased electrostatic field strength for all industrial dust samples tested, regardless of fabric type and other relevant parameters.     

Pilot plant/full scale EP system design and performance on a BOF application

An ESP pilot plant study was done on emissions from a BOF process which is cyclic with very high and low gas volumes, temperature and grain loadings. Data collected were EP performance vs. gas velocity, and collection area. Also measured was particle size distribution, dust resi opacity at the EP outlet. From this data, a full size EP system was designed and installed. Recent performance tests indicate the data agrees well with the initial pilot plant study. Emissions have been reduced from 11 grs/scf (27.1 g/m³) to less than 0.033 grs/scf (81 mg/m³) and opacity to 20% or less.     

Chlorinated paraffins in indoor air and dust: concentrations, congener patterns, and human exposure

Chlorinated paraffins (CPs) are large production volume chemicals used in a wide variety of commercial applications. They are ubiquitous in the environment and humans. Human exposure via the indoor environment has, however, been barely investigated. In the present study 44 indoor air and six dust samples from apartments in Stockholm, Sweden, were analyzed for CPs, and indoor air concentrations are reported for the first time. The sumCP concentration (short chain CPs (SCCPs) and medium chain CPs (MCCPs)) in air ranged from <5-210 ng m(-3) as quantified by gas chromatography coupled to electron ionization tandem mass spectrometry (GC/EI-MS/MS). Congener group patterns were studied using GC with electron capture negative ionization MS (GC/ECNI-MS). The air samples were dominated by the more volatile SCCPs compared to MCCPs. SumCPs were quantified by GC/EI-MS/MS in the dust samples at low μg g(-1) levels, with a chromatographic pattern suggesting the prevalence of longer chain CPs compared to air. The median exposure to sumCPs via the indoor environment was estimated to be ~1 μg day(-1) for both adults and toddlers. Adult exposure was dominated by inhalation, while dust ingestion was suggested to be more important for toddlers. Comparing these results to literature data on dietary intake indicates that human exposure to CPs from the indoor environment is not negligible.     

Maximum power point tracking methods for photovoltaic systems operating under partially shaded or rapidly variable insolation conditions: a review paper

To increase the efficiency of photovoltaic (PV) systems, maximum power point (MPP) tracking of the solar arrays is needed. Under partially shaded conditions (PSCs), the solar arrays power–current (P–I) characteristic has multiple MPP. This paper presents various methods and approaches of tracking the MPP from a PV generator operating under PSC. Some comparisons, advantages, drawbacks and critical analysis of each method are discussed. It was found that, indirect methods use empirical data or mathematical expressions of numerical approximations to estimate the MPP from the PV generator’s voltage, current and irradiance. Direct methods offer the advantage of obtaining the actual maximum power from the PV generator’s voltage and current. Artificial intelligence methods do not need exact mathematical models. They can perform under parameter variation, load and supply voltage disturbances. Finally, novel methods require less number of iterations to converge, independent to the initial conditions. All these algorithms can be included in some of the DC/DC converters and MPP trackers for stand-alone or grid-connected systems.     

Linking high resolution mass spectrometry data with exposure and toxicity forecasts to advance high-throughput environmental monitoring

There is a growing need in the field of exposure science for monitoring methods that rapidly screen environmental media for suspect contaminants. Measurement and analysis platforms, based on high resolution mass spectrometry (HRMS), now exist to meet this need. Here we describe results of a study that links HRMS data with exposure predictions from the U.S. EPA's ExpoCast™ program and in vitro bioassay data from the U.S. interagency Tox21 consortium. Vacuum dust samples were collected from 56 households across the U.S. as part of the American Healthy Homes Survey (AHHS). Sample extracts were analyzed using liquid chromatography time-of-flight mass spectrometry (LC–TOF/MS) with electrospray ionization. On average, approximately 2000 molecular features were identified per sample (based on accurate mass) in negative ion mode, and 3000 in positive ion mode. Exact mass, isotope distribution, and isotope spacing were used to match molecular features with a unique listing of chemical formulas extracted from EPA's Distributed Structure-Searchable Toxicity (DSSTox) database. A total of 978 DSSTox formulas were consistent with the dust LC–TOF/molecular feature data (match score ≥ 90); these formulas mapped to 3228 possible chemicals in the database. Correct assignment of a unique chemical to a given formula required additional validation steps. Each suspect chemical was prioritized for follow-up confirmation using abundance and detection frequency results, along with exposure and bioactivity estimates from ExpoCast and Tox21, respectively. Chemicals with elevated exposure and/or toxicity potential were further examined using a mixture of 100 chemical standards. A total of 33 chemicals were confirmed present in the dust samples by formula and retention time match; nearly half of these do not appear to have been associated with house dust in the published literature. Chemical matches found in at least 10 of the 56 dust samples include Piperine, N,N-Diethyl-m-toluamide (DEET), Triclocarban, Diethyl phthalate (DEP), Propylparaben, Methylparaben, Tris(1,3-dichloro-2-propyl)phosphate (TDCPP), and Nicotine. This study demonstrates a novel suspect screening methodology to prioritize chemicals of interest for subsequent targeted analysis. The methods described here rely on strategic integration of available public resources and should be considered in future non-targeted and suspect screening assessments of environmental and biological media.     

Tubular electrostatic precipitators of two-stage design

Although the “two stage” electrostatic precipitator concept was first developed in 1910, until recently most of their use was confined to in-plant air cleaning. In the last decade, plate type designs have been modified to make them suitable for industrial applications involving organic emissions, most notably in asphalt saturating, plastic curing, food processing, printing, textile finishing, and heat treating industries. However, plate type designs are inadequate in applications where very high loading and/or high particulate content are involved.Tubular design with wider spacing and higher voltages incorporates the best features of both the single stage and two stage type precipitators. These units have been used in molybdenum roasting, zirconium calcining, ammonia scrubbing of oxides of sulfur, meat broiling, foundry exhaust, etc.The paper discusses design parameters, field test data, and operating data on these units. Comparisons with single-stage type precipitators are made wherever applicable. Advantages and disadvantages of two stage precipitators are also discussed.     

Energy and exergy analysis of a PCM-based solar powered winter air conditioning using desiccant wheel during nocturnal

In this paper, heating and humidification of air for space have been carried out by using a phase change material (PCM)-based solar-powered desiccant wheel air conditioning (SPDWAC) in winter. The analysis of the setup has been done at different air flow rates. At low and high air flow rates, system has mean thermal coefficient of performance of 0.121 and 0.172, respectively, and mean exergy efficiency of 0.0787 and 0.0846, respectively. The mean thermal coefficient of performance of the system at high air flow rate (127.23 kg h-1) is 1.42 times the low air flow rate (63.62 kg h-1) and average exergy efficiency of the system at high air flow rate is 1.07 times the low air flow rate. It is observed that with an increase in air flow rate, efficiency of the evacuated tube solar air collector (ETSAC) increases. The average efficiency of the ETSAC at high air flow rate is 15.60%. The maximum average energy efficiency (17.80%) and exergy efficiency (17.08%) of the PCM storage system have been obtained at high air flow rate. The overall performance of the system showed that the use of PCM storage is feasible to run the system in winter during the hours of darkness.     

Aerosol filtration by a cocurrent moving granular bed: Penetration mechanisms

An experimental apparatus has been constructed to investigate aerosol filtration by a cocurrent moving granular bed filter (CMGBF). In a CMGBF, aerosol passes downward through a descending bed of dirty granules while clean granules are added continously at the bed top. The effect of an intergranular dust deposit on penetration in a CMGBF was investigated in a 2⁴ factorial experiment in which the control variables were superficial gas velocity (100 and 250 mm/s), bed depth (130 and 230 mm), granule size (2.1 and 2.7 mm), and the intergranular dust deposit expressed as percent by weight of collected dust in the bed (1% and 5%). All tests were conducted at ambient temperature and pressure using resuspended utility boiler fly ash as the test aerosol.Mass penetration data identified two major penetration mechanisms: (1) straight through penetration and (2) reentrainment due to granular motion. A static, intergranular dust deposit produced high filtration efficiency (>99%) at the low superficial velocity. When the bed was moving, reentrainment of collected dust was significant and accounted for about three-quarters of the penetrating dust. Particle size analyses reveal that the two penetration mechanisms are size dependent. Most particles larger than about one micrometer in diameter that penetrate the CMGBF do so by reentrainment after being collected initially. Virtually no particles smaller than about 0.3 μm in diameter penetrate by reentrainment; when these small particles penetrate, they pass straight through without being collected.     

Selenium and exposure to fibrogenic mineral dust: A mini-review

Individuals exposed to fibrogenic mineral dust may exhibit an impaired antioxidant system and produce high levels of reactive oxygen and nitrogen species through immune cells, contributing to the perturbation of immune cell function, inflammation, fibrosis and lung cancer. The lung diseases which are caused by inhalation of fibrogenic mineral dust, known as pneumoconioses, develop progressively and irreversibly over decades. At the moment there is no known cure. The trace element selenium has potent antioxidant and anti-inflammatory properties mediated mainly through selenoproteins. Research has demonstrated that selenium has the ability to protect against cardiovascular diseases; to kill cancer cells in vitro and reduce cancer incidence; and to immunomodulate various cellular signaling pathways. For these reasons, selenium has been proposed as a promising therapeutic agent in oxidative stress associated pathology that in theory would be beneficial for the prevention or treatment of pneumoconioses such as silicosis, asbestosis, and coal worker's pneumoconiosis. However, studies regarding selenium and occupational lung diseases are rare. The purpose of this study is to conduct a mini-review regarding the relationship between selenium and exposure to fibrogenic mineral dust with emphasis on epidemiological studies. We carried out a systematic literature search of English published studies on selenium and exposure to fibrogenic mineral dust. We found four epidemiological studies. Reviewed studies show that selenium is lower in individuals exposed to fibrogenic mineral dust. However, three out of the four reviewed studies could not confirm cause-and-effect relationships between low selenium status and exposure to fibrogenic mineral dust. This mini-review underscores the need for large follow-up and mechanistic studies for selenium to further elucidate its therapeutic effects.     

中国能源经济效率动态分析及预测

能源经济效率的影响因素作用复杂,系统各要素之间存在复杂的动态关系.本文利用中国1978-2007年的实际数据,应用向量自回归模型(Vector Auto-regression,VAR)、脉冲响应分析、协整理论等计量理论与方法对中国能源经济效率的变动进行动态实证分析,并预测中国能源经济效率的发展趋势.结果表明,中国的能源经济效率、第三产业比重和能源价格指数之间存在协整关系,从长期来看,1%的第三产业结构或者能源价格变化可以分别给能源经济效率带来0.3477%和0.4.785%的同方向变化;除了产业结构对能源价格短期响应之外,变量之间都是正向的冲击响应,滞后6-10期响应达到最大值,之后逐渐趋于稳定:依据VAR模型动态预测结果,未来10年中国能源经济效率发展趋势不容乐观,由于系统较长的滞后响应期,近几年能源经济效率、能源价格和产业结构的变动会在未来较长时间内对能源经济效率的提升产生不利影响,应当及时调整能源经济策略.     

Diesel particulate extracts in bacterial test systems

The Ames bacterial mutagenicity test system was used to evaluate parameters which may affect the mutagenic activity of diesel particulate extracts. The optimal extraction conditions, extractability of mutagens by simulated biological fluids and the effect of collection method were investigated. The role of solvent was examined by extracting diesel particles with methanol, acetone, cyclohexane, ethyl acetate, n-hexane, dichloromethane, benzene and a benzene-ethanol mixture. Of these, the dichloromethane extract exhibited the highest activity in the Ames test, although methanol yielded the largest extractable mass. Diesel particles were also extracted by dimethyl sulfoxide (DMSO) and four other simulated biological fluids for 48 h at 25, 37, and 45°C to study the effects of temperature. The mutagenic activity of the DMSO extract began to decline at temperatures higher than 37°C after 8 h of incubation. Fetal calf serum was the only simulated biological fluid which eluted mutagenic activity from the particles. No activity was detected in the 0.5% bovine serum albumin, simulated lung surfactant and saline extracts. Diesel particles collected by electrostatic precipitation (ESP) and filtration were studied. The mutagenic activities of both extracts were comparable when expressed as revertants per mg of particle. After the extracts were separated into nine fractions by a solvent partitioning scheme, the majority of the activity was found in the neutral-nonpolar II, neutral polar, strong acid and weak acid fractions. The acid salt fraction from the ESP sample was inactive. These results demonstrate that differences in the extraction conditions can result in differences in the mutagenic activity of diesel particulate extract. Since the mutagens in the extracts are not readily extractable by simulated biological fluids, the question of bioavailability of mutagens in diesel particles must be considered in the final assessment of their potential effects in biological systems and organisms.     

电网发展、清洁电源接入与地区能源效率

鉴于我国已经建成全球规模最大的超高压和特高压电网,彻底弥补了电力跨区配置的电网基础设施短板,并且为清洁电源并入电网和跨区消纳提供了完善的基础设施,不仅克服我国电力负荷中心和能源基地的区域布局不协调,而且有益于缓解日益严峻的能源利用率低下和环境污染问题。本文利用1991—2012年全国29个省市面板数据实证研究了清洁电源并网对地区全要素能源效率的影响。为保证实证结果稳健性分别在线性和非线性实证框架下采用系统广义矩估计(SYS-GMM)和面板平滑转换模型(PSTR)两种方法估计了清洁电源接入高压、超高压和特高压电网的地区全要素能源效率异质性效应。实证结果显示:(1)我国电网基础设施对地区全要素能源效率具有明显的增进效应,特别是超高压电网在促进全要素能源效率提升上表现的最为突出,在特高压骨干网架尚未形成的情况下起到了支柱性作用。(2)高压、超高压、特高压与清洁电源交互项的估计系数始终位于负数区间,反映清洁电源并网的能源效率绩效并不明显,受限于并网规模和机制缺陷,还没有发挥出全要素能源效率提升作用。(3)随着人均GDP的不断提高,各等级电网对地区能源效率的益处越来越明显,并且存在着门槛效应。(4)特高压电网对地区能源效率的积极作用主要表现在东部沿海高收入省份,这些省份作为电力消费负荷中心,大规模接入清洁电源对能源效率改善裨益明显。接下来,需要根据地区的能源禀赋结构选择清洁电源的并网模式,完善的电网基础设施、合理的电源结构还需要配置以高效的清洁电源并网机制才能不断增进地区全要素能源效率。     

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.