Mass transfer within electrostatic precipitators: trace gas adsorption by sorbent-covered plate electrodes

Varying degrees of mercury (Hg) capture have been reported within the electrostatic precipitators (ESPs) of coal-fired electric utility boilers. There has been some speculation that the adsorption takes place on the particulate-covered plate electrodes. This convective mass transfer analysis of laminar and turbulent channel flows provides the maximum potential for Hg adsorption by the plate electrodes within an ESP under those conditions. Mass transfer calculations, neglecting electrohydrodynamic (EHD) effects, reveal 65% removal of elemental Hg for a laminar flow within a 15-m-long channel of 0.2-m spacing and 42% removal for turbulent flow within a similar configuration. Both configurations represent specific collection areas (SCAs) that are significantly larger than conventional ESPs in use. Results reflecting more representative SCA values generally returned removal efficiencies of <20%. EHD effects, although potentially substantial at low Reynolds numbers, diminish rapidly with increasing Reynolds number and become negligible at typical ESP operating conditions. The present results indicate maximum Hg removal efficiencies for ESPs that are much less than those observed in practice for comparable ESP operating conditions. Considering Hg adsorption kinetics and finite sorbent capacity in addition to the present mass transfer analyses would yield even lower adsorption efficiencies than the present results. In a subsequent paper, the author addresses the mass transfer potential presented by the charged, suspended particulates during their collection within an ESP and the role they potentially play in Hg capture within ESPs.     

Relationship of Particulate Control,SO2 Removal,and Waste Management

Results with the EPRI 2.5 MW(e) Integrated Environmental Control Pilot Plant (IECPP) indicate the interrelationship of particulate penetration, SO₂ scrubber operation, waste production, and waste properties. Tests compared a fabric filter/wet scrubber and ESP/wet scrubber, the latter operated to simulate 1979 New Source Performance Standards (NSPS), 1971 NSPS, and pre-NSPS ESP units. Tests were conducted with low-sulfur coal producing a flue gas concentration of400ppm; flue gas spiking could be used to increase SO₂ to 2000 ppm. Scrubber waste was dewatered in a thickener and vacuum belt filter (to 55 percent solids content), and mixed with fly ash. The pilot SO₂ scrubber—when preceded by an ESP and forced to operate in zero-discharge—captured less SO₂ than when preceded by a fabric filter. Also, scrubber operation with the ESP produced a greater quantity of waste with difficult handling characteristics, as compared to operation with the fabric filter. These difficulties occurred with particulate penetration above 0.10 lb/MBtu, which could reduce reagent utilization to 80percent. These results are attributable to inhibited limestone dissolution due to accumulation of an aluminum/fluoride compound. For both lowsulfur and simulated high-sulfur test conditions, allowing wastewater discharge to purge aluminum/fluoride content restored performance to design levels. Particulate control efficiency also affected solid waste physical properties. The fabric filter/wet scrubber produced the lowest solid waste permeability (10^?8 cm/s). ESP operation at 1979 NSPS and pre-1971 NSPS ESPs increased solid waste permeability to 10^?7 and 10^?6 cm/s, respectively. These results are meaningful for SO₂ scrubbers both for new plants and for retrofit to units with pre-NSPS ESPs, and could become significant with the increasing trend to restricted water discharge.     

Novel hybrid composite discharge electrode for electrostatic precipitator

Over the last few decades, electrostatic precipitators (ESPs) have emerged as effective air pollution control devices for treating coal-fired power plant exhausts. Among the components of the ESP, the discharge electrodes are extremely important in determining the collection efficiency of the ESP. Typically, in wet ESPs, the discharge electrodes used must be made of corrosion-resistant alloys, which makes them extremely expensive and heavy. Hybrid composite discharge electrodes have the potential to be lightweight and corrosion-resistant substitute for traditional metal alloy electrodes used in wet ESPs. In this experimental study, a novel hybrid composite electrode (recently patented at Ohio University) is presented as a substitute for traditional metal electrodes in wet ESPs. The samples of hybrid electrodes were fabricated by using carbon fiber composites, combined with metal mesh, in the shape of a long and thin tape. The electrode’s electrical response was evaluated in open atmospheric conditions, while connected to a transformer-rectifier unit to generate a corona current at voltages exceeding 50 kV. Results of these hybrid electrodes were compared with traditional metal electrodes. The hybrid composite discharge electrode produced a uniform corona at comparable power levels to that of metal electrodes, with additional advantages of being compact, lightweight, and highly corrosion resistant. In addition, hybrid composite electrodes exhibited lower corona onset voltage as compared with metal electrodes. The preliminary experimental data are encouraging and show significant potential for this new inexpensive hybrid electrode to replace metal electrodes in wet ESPs, providing comparable (and in some cases exceeding) collection efficiencies with lower ozone generation.

Implications: The newly invented hybrid composite electrode (HCE) performance was evaluated through experimentation with conventional metal electrodes. The HCE performance was comparable to the metal electrodes. The HCE also exhibited uniform corona fields and steady power while maintaining similar and in some cases superior electrical performance as compared with metal electrodes and thus shows a significant potential to substitute metal electrodes in wet ESP systems.     

Issues and Trends in Electrostatic Precipitation Technology for U.S. Utilities

The pace and direction of electrostatic precipitator (ESP) technology evolution in the United States will be governed by two key forces. The first is new clean air legislation passed by the U.S. Congress and signed by President Bush on November 15,1990. This law requires electric utilities to further reduce SO₂ and NO_x emissions, which may impact particulate controls. In addition, very fine (< 10 micron) participates and potentially toxic trace emissions from utility power plants may be regulated. The second major factor is the expected upsurge in new plant construction beginning in the late 1990s. Together, these forces should define the performance requirements and market for new ESPs.

This paper identifies and briefly describes technologies that the Electric Power Research Institute (EPRI) is developing to help U.S. utilities meet these challenges cost-effectively. Among the technologies addressed are: advanced digital voltage controls, flue gas conditioning, intermittent energization, temperature-controlledprecharging (i.e., two-stage ESP), wide plate spacing, positive energization of corona electrodes for hot-side ESPs, and integration of conventional ESPs with pulse-jet baghouses.     

Fine particle migration and collection in a wet electrostatic precipitator

Electrostatic precipitation is considered as an effective technology for fine particle removal. A lab-scale wet electrostatic precipitator (ESP) with wire-to-plate configuration was developed to study particle migration and collection. The performance of the wet ESP was evaluated in terms of the corona discharge characteristics, total removal efficiency and fractional removal efficiency. The corona discharge characteristics and particle removal abilities of the wet ESP were investigated and compared with dry ESP. Particle removal efficiency was influenced by discharge electrode type, SO₂ concentration, specific collection area (SCA) and particle/droplet interaction. Results showed that the particle removal efficiency of wet ESP was elevated to 97.86% from 93.75% of dry ESP. Three types of discharge electrodes were investigated. Higher particle removal efficiency and larger migration velocity could be obtained with fishbone electrode. Particle removal efficiency decreased by 2.87% when SO₂ concentration increased from 0 ppm to 43 ppm as a result of the suppression of corona discharge and particle charging. The removal efficiency increased with higher SCA, but it changed by only 0.71% with the SCA increasing from 25.0 m²/(m³/s) to 32.5 m²/(m³/s). Meanwhile, the increasing of particle and droplet concentration was favorable to the particle aggregation and improved particle removal efficiency.

Implications: This work tends to study the particle migration and collection under spraying condition. The performance of a wet electrostatic precipitator (ESP) is evaluated in terms of the corona discharge characteristics, total particle removal efficiency, and fractional particle removal efficiency. The effects of water droplets on particle removal, especially on removal of particles with different sizes, is investigated. The optimization work was done to determine appropriate water consumption, discharge electrode type, and specific collection area, which can provide a basis for wet ESP design and application.     

PCDDs, PCDFs emission control by dry scrubbing system

Presently, in Japan there are no limitations on the emission of PCDDs or PCDFs, but in order to study the feasibility of dry type air pollution control, a pilot plant was constructed in 1988 and the removal efficiencies for PCDDs, acid gas and heavy metals were measured.At the same time PCDDs concentration was compared with that of a previously installed electrostatic precipitator (ESP) plus wet scrubber line.In this paper, the following two items are reported.

1. (1) The difference in the amounts of PCDDs and PCDFs produced due to differences in gas temperature and retention time in ESP and fabric filter (FF).

2. (2) Removal efficiencies of PCDDs and PCDFs of fabric filter.

PCDDs concentration, generally 100–200 ng/Nm³ at the boiler outlet (ESP inlet and/or Quench Reactor (QR) inlet), increased several times at the ESP outlet, but it showed almost no increase at the QR outlet due to a sudden temperature drop. The temperature was 280–310°C, and the gas retention time was 12 sec. during passage through ESP so that it is thought that PCDD was formed under these conditions.On the other hand, a removal efficiency of approx. 90% was obtained with the fabric filter, and the PCDD at the bag outlet was at a sufficiently low level.     

Integration of a nonmetallic electrostatic precipitator and a wet scrubber for improved removal of particles and corrosive gas cleaning in semiconductor manufacturing industries

To remove particles in corrosive gases generated by semiconductor industries, we have developed a novel non-metallic, two-stage electrostatic precipitator (ESP). Carbon brush electrodes and grounded carbon fiber-reinforced polymer (CFRP) form the ionization stage, and polyvinyl chloride collection plates are used in the collection stage of the ESP The collection performance of the ESP downstream of a wet scrubber was evaluated with KC1, silica, and mist particles (0.01-10 pm), changing design and operation parameters such as the ESP length, voltage, and flow rate. A long-term and regeneration performance (12-hr) test was conducted at the maximum operation conditions of the scrubber and ESP and the performance was then demonstrated for 1 month with exhaust gases from wet scrubbers at the rooftop of a semiconductor manufacturing plant in Korea. The results showed that the electrical and collection performance of the ESP (16 channels, 400x400 mm2) was maintained with different grounded plate materials (stainless steel and CFRP) and different lengths of the ionization stage. The collection efficiency of the ESP at high air velocity was enhanced with increases in applied voltages and collection plate lengths. The ESP (16 channels with 100 mm length, 400x400 mm2x540 mm with a 10-mm gap) removed more than 90% of silica and mistparticles with 10 and 12 kV applied to the ESPat the air velocity of 2 m/s and liquid-to-gas ratio of 3.6 L/m3. Decreased performance after 13 hours ofcontinuous operation was recovered to the initial performance level by 5 min of water washing. Moreover during the 1-month operation at the demonstration site, the ESP showed average collection efficiencies of 97% based on particle number and 92% based on total particle mass, which were achieved with a much smaller specific corona power of 0.28 W/m3/hr compared with conventional ESPs.     

Electrostatic Stimulation of Fabric Filtration

The concept of electrostatic stimulation of fabric filtration (ESFF) has been investigated at pilot scale. The pilot unit consisted of a conventional baghouse in parallel with an ESFF baghouse, allowing direct comparison. All results reported in this paper are for pulse-cleaned bags in which the electric field was maintained parallel to the fabric surface. The performance of the ESFF baghouse has been superior to the parallel conventional baghouse by several measures. The ESFF baghouse demonstrated: (1) a reduced rate of pressure drop increase during a filtration cycle, (2) lower residual pressure drop, (3) stable operation at higher face velocities, and (4) improved particle removal efficiency. These benefits can be obtained with only minor modifications to conventional pulse-jet hardware and at low electrical power consumption. The indicated ability to operate at increased face velocities with only modest expenditure for electrical hardware leads to very favorable economic projections.     

容积负荷对ANAMMOX生物滤池脱氮效能的影响及其基质动力学

采用2套启动成功的上向流厌氧氨氧化（ANAMMOX）生物滤柱，通过调节进水NaNO₂和（NH₄）₂SO₄ 的浓度负荷及水力负荷，改变进水容积负荷，探讨容积负荷对ANAMMOX生物滤柱脱氮效能的影响及其动力学模型。结果表明，滤速恒定条件下，通过提高进水基质浓度来提高进水TN容积负荷，其容积负荷去除动力学过程符合Monod-Haldane基质抑制模型。进水NH₄⁺-N与NO₂^--N浓度分别低于100 mg/L和133 mg/L时，反应器脱氮效果不受明显影响，TN容积去除负荷可达4.21 kg/（m³·d），TN去除率可达80%以上。进水基质浓度恒定条件下，通过提高滤速来提高进水TN容积负荷，其容积负荷去除动力学过程符合零级动力学方程。不受基质浓度抑制的条件下，滤速为3.0 m/h、进水容积负荷为8.82 kg/（m³·d）时，反应器总氮容积负荷去除量可达7.15 kg/（m³·d），总氮去除率可达81.1%。     

Economic Comparison of Selected Scenarios for Electrostatic Precipitators and Fabric Filters

Compliance with particulate standards for utility boilers burning low sulfur western coal has resulted in the installation and proposed installation of several fabric filter collectors where cold or hot electrostatic precipitators would have traditionally been applied. Recently, SO3 conditioning has been used to improve cold precipitator performance resulting in considerable reduction in specific collection area (SCA). All this suggests that trade-offs exist indicating ranges of SCA, A/C ratio, and power plant size (Mw) where fabric filters become competitive with electrostatic precipitators. Conceptual cost models are presented which indicate total capital investment and annual costs for the control devices. Precipitator costs are correlated with collecting area, gas flow rate, and power input and are presented as functions of SCA and Mw. Fabric filter costs are keyed to gross filter area, pressure drop, and gas flow rate. Fabric filters become competitive when a cold precipitator requires SCAs in excess of 600 to 800 and competitive when a hot precipitator requires equivalent cold precipitator SCAs in excess of 600 to 1000 depending on A/C ratio, Mw, and hot precipitator SCA credit allowance. The S0₃ conditioned precipitator scenario is shown to be economically competitive with fabric filters.     

纤维与石英砂过滤技术的比较研究

提出了无需额外反冲洗装置与动力消耗的水力自清洗纤维过滤技术,与石英砂过滤进行了比较研究,探索该技术应用的可行性。结果表明,10 m/h滤速下纤维过滤与石英砂过滤相比,出水浊度、SS分别降低59%和86%,COD、TOC、TP和TN降低5%～20%,水头损失大幅降低,两者初始水头损失分别为0.12 kPa和3.97 kPa,5 h后分别达到1.58kPa和5.98 kPa。纤维滤柱反冲洗历时40 s,而石英砂滤柱为15 min,反洗耗水率分别为2.9%和6.9%。反洗后纤维滤柱出水浊度和SS分别为4.08 NTU、6 mg/L,低于石英砂滤柱的5.81 NTU、28 mg/L。水力自清洗纤维过滤技术可节省动力装置和动力消耗,反冲洗历时短、耗水率低,具有较好的应用前景。     

Effect of Cuscuta campestris parasitism on the physiological and anatomical changes in untreated and herbicide-treated sugar beet

The effects of field dodder on physiological and anatomical processes in untreated sugar beet plants and the effects of propyzamide on field dodder were examined under controlled conditions. The experiment included the following variants: N—noninfested sugar beet plants (control); I - infested sugar beet plants (untreated), and infested plants treated with propyzamide (1500 g a.i. ha^?1 (T₁) and 2000 g a.i. ha^?1(T₂)). The following parameters were checked: physiological—pigment contents (chlorophyll a, chlorophyll b, total carotenoids); anatomical -leaf parameters: thickness of epidermis, parenchyma and spongy tissue, mesophyll and underside leaf epidermis, and diameter of bundle sheath cells; petiole parameters: diameter of tracheid, petiole hydraulic conductance, xylem surface, phloem cell diameter and phloem area in sugar beet plants. A conventional paraffin wax method was used to prepare the samples for microscopy. Pigment contents were measured spectrophotometrically after methanol extraction. All parameters were measured: prior to herbicide application (0 assessment), then 7, 14, 21, 28 and 35 days after application (DAA). Field dodder was found to affect the pigment contents in untreated sugar beet plants, causing significant reductions. Conversely, reduction in the treated plants decreased 27% to 4% for chlorophyll a, from 21% to 5% for chlorophyll b, and from 28% to 5% for carotenoids (T₁). Also, in treatment T_2, reduction decreased in infested and treated plants from 19% to 2% for chlorophyll a, from 21% to 2% for chlorophyll b, from 23% to 3% for carotenoids and stimulation of 1% and 2% was observed 28 and 35 DAA, respectively. Plants infested (untreated) by field dodder had lower values of most anatomical parameters, compared to noninfested plants. The measured anatomical parameters of sugar beet leaves and petiole had significantly higher values in noninfested plants and plants treated with propyzamide than in untreated plants. Also, the results showed that propyzamide is an adequate herbicide for control of field dodder at the stage of early infestation.     

收尘区脉冲供电对电除尘器收集性能的影响

建立了双区电除尘器实验模型,研究了预荷电压、不同供电方式下极板间距、电极型式对双区电除尘器收尘效果的影响.结果表明:随着预荷电压逐渐升高,除尘效率也随之增加,双区除尘效果明显优于单区的除尘效果.脉冲供电对电除尘器的除尘性能影响明显,与直流供电相比,脉冲供电对PM25的分级效率可提高16.9%;在较高的电压时,极板间距为...     

乌梁素海湖滨带盐碱土碱化参数与特征分析

为了研究乌梁素海湖滨带,不同植被的土壤盐碱特征,测定了乌梁素海湖滨带盐碱土的碱化度(ESP)、钠吸附比(SAR)、总碱度、pH值和含盐量等指标,分析了该类型的土壤的简化特征及其垂直分布态势.结果表明,乌梁素海湖滨带土壤可溶件例子组成以Na+、SO2-4-和Cl-为主,各土层中Na+占阳离子总量比例平均多在63.6%以上...     

Simulation of Stack Plume Opacity

ABSTRACT

The visual impact of primary particles emitted from stacks is regulated according to stack opacity criteria. In-stack monitoring of the flue gas opacity allows plant operators to ensure that the plant meets U.S. Environmental Protection Agency opacity regulations. However, the emission of condensable gases such as SO₃ (that hydrolyzes to H₂SO₄), HCl, and NH₃, which may lead to particle formation after their release from the stack, makes the prediction of stack plume opacity more difficult.

We present here a computer simulation model that calculates the opacity due to both primary particles emitted from the stack and secondary particles formed in the atmosphere after the release of condensable gases from the stack. A comprehensive treatment of the plume rise due to buoyancy and momentum is used to calculate the location at which the condensed water plume has evaporated (i.e., where opacity regulations apply).

Conversion of H₂SO₄ to particulate sulfate occurs through nucleation and condensation on primary particles. A thermodynamic aerosol equilibrium model is used to calculate the amount of ammonium, chloride, and water present in the particulate phase with the condensed sulfate. The model calculates the stack plume opacity due to both primary and secondary particles. Examples of model simulations are presented for three scenarios that differ by the emission control equipment installed at the power plant: (1) electrostatic precipitators (ESP), (2) ESP and flue gas desulfurization, and (3) ESP and selective catalytic reduction. The calculated opacity is most sensitive to the primary particulate emissions. For the conditions considered here, SO₃ emissions showed only a small effect, except if one assumes that most H₂SO₄ condenses on primary particles. Condensation of NH₄Cl occurs only at high NH₃ emission rates (about 25 ppm stack concentration).     

The impact of transportation control measures on emission reductions during the 2008 Olympic Games in Beijing,China

Traffic congestion and air pollution were two major challenges for the planners of the 2008 Olympic Games in Beijing. The Beijing municipal government implemented a package of temporary transportation control measures during the event. In this paper, we report the results of a recent research project that investigated the effects of these measures on urban motor vehicle emissions in Beijing. Bottom–up methodology has been used to develop grid-based emission inventories with micro-scale vehicle activities and speed-dependent emission factors. The urban traffic emissions of volatile organic compounds (VOC), carbon monoxide (CO), nitrogen oxides (NO_x) and particulate matter with an aerodynamic diameter of 10 μm or less (PM₁₀) during the 2008 Olympics were reduced by 55.5%, 56.8%, 45.7% and 51.6%, respectively, as compared to the grid-based emission inventory before the Olympics. Emission intensity was derived from curbside air quality monitoring at the North 4th Ring Road site, located about 7 km from the National Stadium. Comparison between the emission intensity before and during the 2008 Olympics shows a reduction of 44.5% and 49.0% in daily CO and NO_x emission from motor vehicles. The results suggest that reasonable traffic system improvement strategies along with vehicle technology improvements can contribute to controlling total motor vehicle emissions in Beijing after the Olympic Games.     

A Fabric Denuder for Sampling Semi-Volatile Species

ABSTRACT

A new style of diffusion denuder has been evaluated specifically for sampling HNO₃. A coated fabric is used as the denuder substrate, which can be loaded directly into a standard filter holder. This approach allows direct denuder sampling with no additional capital costs over filter sampling and simplifies the coating and extraction process.

Potential denuder materials and coatings were evaluated in the laboratory to test the removal efficiency. NaCl coatings were used to assess more than 20 materials for HNO₃ collection efficiency. Particle retention, which would cause a denuder to have a positive bias for gas concentration measurements, was evaluated by ambient air sampling using particulate sulfate as the reference aerosol. Particle retention varied from 0 to 15%, depending on the denuder material tested. The best performing material showed an average particle retention of less than 3%.

Denuder efficiency of four fabric materials was tested under ambient conditions to determine removal efficiency. The fabric denuder method was compared with a long path-length Fourier transform infrared (FTIR) spectrometer, a tunable diode laser absorption spectrometer (TDLAS), and a denuder difference sampler to independently measure HNO₃. HNO₃ collection efficiency was typically 90% for the denuders, whether coated with NaCl or not. For 10-L/min sampling rates with the fabric denuder, the square of the correlation coefficient with the FTIR spectrometer was 0.73, compared to 0.24 with the TDLAS.     

Effect of matrix on the electrochemical characteristics of TiO2 nanotube array-based PbO2 electrode for pollutant degradation

A series of lead dioxide electrodes developed on titania nanotube arrays with different matrix were fabricated by electrodeposition. Before the deposition of PbO₂, the matrix of this anode was electrochemically reduced in (NH₄)₂SO₄ solution and/or pre-deposited with certain amounts of copper. To gain insight into these pretreatments, the PbO₂ electrodes were characterized by SEM, LSV, and XRD, and their electrocatalytic activities for pollutant degradation were compared using p-nitrophenol (p-NP) as a model. It was confirmed that the electrochemical reduction with (NH₄)₂SO₄ resulted in the partial conversion of TiO₂ into Ti₄O₇ and Ti₅O₉, which increased the conductivity of PbO₂ anode, but decreased its electrochemical activity, while the Ti/TNTs*-Cu/PbO₂ electrode with both pretreatments possessed the highest oxygen evolution overpotential of 2.5 V (vs. SCE) and low substrate resistance. After a 180-min treatment on this electrode, the removal efficiency of p-NP reached 82.5 % and the COD removal achieved 42.5 % with the energy consumption of 9.45 kWh m^?3, demonstrating the best performance among these electrodes with different matrices. Therefore, this titania nanotube array-based PbO₂ electrode has a promising application in the industrial wastewater treatment.     

Fabric Filtration for Fly Ash Control

Economic projections and the growing experience with more diverse baghouse applications indicate that fabric filtration will become an even more popular type of control technology. While the fabric filter market shows signs of great promise now, an especially significant upturn is predicted within the next half dozen years when dry scrubbing becomes the primary process for combined S0₂ and par-ticulate control. In the interim, with more and more utility and industrial boilers gaining experience with baghouses, this control method can be expected to develop as an even more acceptable technique, especially on low S coal burning units. Nevertheless, the users stress the need for conservative planning and designing, giving extra care to start-up and maintenance procedures.     

泛比电阻电除尘器收尘性能实验研究

泛比电阻电除尘器是一种具有辅助电极和交错平板收尘电极的新型电除尘器.通过对其伏安特性及除尘效率的试验研究,并与传统线板式静电除尘器进行比较,结果表明辅助电极对电晕电流具有明显的抑制作用,在相同的外加电压下,泛比电阻电除尘器对高比电阻锅炉飞灰的收尘效率比普通的线板式电除尘器明显要高.