Fabric Filter Technology for Utility Coal-Fired Power Plants

This is the sixth and last part in a series of papers discussing the experience of electric utilities in applying baghouse technology for the collection of particulate matter at coal-fired electric power generating plants. The series presents new data obtained in research sponsored by the Electric Power Research Institute (EPRI) on reverse-gas and shake/deflate cleaned baghouses, and specifically addresses a number of unresolved issues in the design and operation of these units. This paper discusses research, development and demonstration activities now underway or planned to further understand baghouse technology to ensure efficient, economic and reliable service in utility applications. In addition, it summarizes the major findings reported in Parts I through V.     

Fabric Filter Technology for Utility Coal-Fired Power Plants

This is the third in a series of papers discussing the experience of electric utilities in applying baghouse technology for the collection of particulate matter at coal-fired electric power generating plants. The series presents new data obtained in research sponsored by the Electric Power Research Institute (EPRI) on reverse-gas and shake/deflate cleaned baghouses, and specifically addresses a number of unresolved issues in the design and operation of these units. This paper provides an overview of the design and operating characteristics of baghouses now in place in the utility industry. In addition, it discusses three key issues in design and operation: the relationships among dust cake weight and chemical composition, air-to-cloth ratio, and pressure drop; fabric selection; and bag life.     

The Potential of Pulse-Jet Baghouses for Utility Boilers. Part 2: Performance of Pulse-Jet Fabric Filter Pilot Plants

Pulse-jet fabric filters (PJFFs) are widely used in U.S. industrial boiler applications and in utility and industrial boilers abroad. Their small size and reduced cost relative to more conventional reverse-gas baghouses makes the use of PJFFs appear to be an attractive particulate control option for utility boilers. This paper (Part 2 of a three-part series) summarizes the results of pilot PJFF studies sponsored by the Electric Power Research Institute at different utility sites in the United States. The purpose of these tests is to evaluate PJFF performance for U.S. fossil-fuel-fired applications. These data are also used to corroborate the results of a recent worldwide survey of PJFF user experience, as described in Part 1 of this series. Part 3 will provide a cost comparison of PJFFs to other particulate control options such as electrostatic precipitators and reverse-gas baghouses.     

Improving Baghouse Performance at the Monticello Generating Station

At the Monticello station, operated by the Texas Utilities Generating Company, lignite coal obtained locally in Titus and Hopkins Counties fuels each of the three units. Units 1 and 2 are identical 575-MW Combustion Engineering (CE) boilers, each of which discharges its effluent to a 36- compartment shake/deflate cleaned baghouse paralleled with four electrostatic precipitators (ESP). Unit 3 is a larger boiler and is followed by an ESP and a scrubber. The Unit 1 and 2 baghouses were designed to clean 80 percent of the flue gas. Since startup, these baghouses have regularly experienced flange-to-flange pressure drops in excess of 10 in. H₂O, with large opacity spikes caused by ash bleeding through the bags after compartment cleanings. Because of higher-than-expected pressure drop, the baghouses receive only about 45-50 percent of the flue gas. Analysis has shown the Monticello lignite ash significantly differs from most other coal ashes. Testing has shown that the Monticello ash is not filtered effectively by many "standard" bag materials. However, this testing indicates that there are fabrics that show promise of eliminating the ash bleedthrough with little pressure drop penalty. Testing has also shown that injection of low concentrations (10-15 ppm) of ammonia (NH₃) into the flue gas significantly decreases ash bleedthrough, so that with NH₃ injection "standard" bag materials may perform adequately. Currently, fullcompartment testing of four fabrics, with and without NH₃ injection, is under way at the Unit 1 baghouse. The research conducted at the Monticello station is reviewed in this paper and the encouraging results from the full-compartment tests are presented.     

The Potential of Pulse-Jet Baghouses for Utility Boilers Part 3: Comparative Economics of Pulse-Jet Baghouse,Precipitators and Reverse-Gas Baghouses

Pulse-jet fabric filters (PJFFs) are widely used in U.S. industrial applications, and in both utility and industrial boilers abroad. Their smaller size and reduced cost relative to more conventional baghouses make PJFFs an attractive particulate control option for utility boilers. This article which is the third in a three-part series, compares the cost of PJFFs with electrostatic precipitators (ESPs) and reverse-gas baghouses (RGBs).

This article presents the capital, operating and maintenance (O&M), and level-ized costs for ESPs, RGBs and PJFFs. The particulate control equipment design and pricing are supplied by manufacturers of the control equipment. A comparison of costs for a base case 250-MW boiler indicates that the PJFF capital cost is 22 percent lower than the cost of an ESP with 400 SCA and 12-inch plate spacing; in addition the PJFF is 35 percent lower than the cost of an RGB. The levelized cost for a PJFF is about equal to the cost of the ESP but 14 percent lower than the cost of the RGB. Overall, the attractiveness of a PJFF versus an ESP depends on the coal type and the outlet emissions limit required. PJFF is favored when low-sulfur coal is fired due to the high-resistivity fly ash. Also, PJFF is favored as more stringent outlet emission rates are required.     

我国汽车排气污染净化研究

本文在调研１９８３年来我国有关汽车排气净化研究的文献基础上，综述了机内净化，机外净化和燃料处理三方面的研究水平与成果，着重探讨了汽车尾气催化净化技术和催化剂的研究。结合我国目前汽车工业和城市机动车污染现状，借鉴国外机动车污染控制的发展道路，提出了我国机动车污染控制技术的发展方向，并对进一步开展汽车排气净化研究提出了建议。     

电凝并式空气净化单元对颗粒物和甲醛净化效果的实验

研究一种新型电凝并式空气净化单元对室内空气中颗粒物和甲醛的净化效果.实验结果表明,高压高频(HV-HF)电凝并装置能促使小粒子相互凝并为较大的电中性的粒子团,这些具有较高比表面积的电中性粒子团进入室内空间,能继续粘附空气中及物体表面上的颗粒,形成更大的粒子团,从而易于被净化单元中的中效过滤器捕集,而且该净化单元对于大粒子(粒径＞0.7μm)浓度较高的场所净化效果更加明显.另外,室内空气中吸附在颗粒物表面的甲醛也随之被高效去除.该净化单元的投入使用,起到了提高过滤效率、去除气溶胶小粒子、降低能耗、进一步改善室内空气品质等多重功效.     

The viability of professional wet cleaning as a pollution prevention alternative to perchloroethylene dry cleaning

The vast majority of dry cleaners worldwide use the toxic chemical perchloroethylene (PCE), which is associated with a number of adverse health and environmental impacts. Professional wet cleaning was developed as a nontoxic alternative to PCE dry cleaning but has not been widely adopted as substitute technology. In the greater Los Angeles, CA, region, a demonstration project was set up to showcase this technology and evaluate its commercial viability by converting seven cleaners from PCE dry cleaning to professional wet cleaning. The demonstration site cleaners who switched to professional wet cleaning were able to maintain their level of service and customer base while lowering operating costs. The cleaners were able to transition to professional wet cleaning without a great degree of difficulty and expressed a high level of satisfaction with professional wet cleaning. Crucial to this success was the existence of the demonstration project, which helped to develop a supporting infrastructure for professional wet cleaning that had otherwise been lacking in the garment care industry.     

Characterization of permanent fouling on the surfaces of UV lamps used for wastewater disinfection.

A significant problem with UV disinfection of wastewater is the accumulation of fouling materials at sleeve-water interfaces. It has been shown that automated chemical and/or mechanical cleaning can remove most fouling materials satisfactorily. However, permanent foulants, which cannot be removed completely by typical cleaning operations, always remain on the quartz sleeves. These permanent foulants reduce UV transmittance, in turn reducing disinfecting effectiveness. This research investigated the origins, formation, and composition of permanent fouling. Four instrumental analyses were used: atomic force microscope (AFM), X-ray fluorescence (XRF), scanning electron microscope combined with energy dispersive X-ray microanalysis (SEM/EDX), and sleeve UV transmittance (SUVT). It appeared that permanent foulants were trapped initially by microscale holes and peaks on fresh sleeve surfaces. Based on the topography and roughness measurements from the AFM, after long-term regular chemical and mechanical cleaning, the wipers of cleaning systems damage sleeve surfaces, creating scratches or holes with larger surface areas. Foulants are trapped more easily, and are attached tightly to the surfaces of these scratches or to each other. The results from XRF and SEM/EDX showed that the main fouling components were aluminum, iron, magnesium, calcium, and phosphorus. These could not be related to wastewater quality. For the specific cases studied, chemical plus mechanical cleaning is more effective in removing foulants and avoiding the accumulation of permanent foulants than mechanical cleaning alone; in most cases, SUVT was higher than 90% after chemical plus mechanical cleaning, whereas mechanical cleaning alone achieved only approximately 30% SUVT after long-term usage.     

基于等离子体反应器的室内空气净化装置研究

在对比若干室内空气净化方法之后 ,介绍了等离子体空气净化的能力、机理以及光催化反应 ,对基于等离子体反应器的室内空气净化典型装置进行系统分析。对等离子体空气净化技术的研究进行了展望 ,指出存在的问题和发展的方向。     

Status and Future of Baghouses in the Utility Industry

Abstract

The cumulative years of service of baghouses in the electric utility industry have doubled since the last industrywide review of their operating performance. We have gathered information from all 102 operating baghouses to develop an updated record of how this technology continues to serve the electric utility industry. In general, baghouse performance has met or exceeded the expectations for controlling emissions. There are, however, wide ranges of pressure drop and bag life performance. Most operators report a long-term trend of increasing pressure drop. The life expectancy of filter bags averages 7.5 years, with more than 20% of the population achieving more than 10 years of bag life. Factors such as coal and ash properties certainly affect baghouse operation, but another reason for variations in bag life is the lack of an optimized protocol for controlling the long-term buildup of residual dustcake. We conclude that many baghouses could operate with lower pressure drop and longer bag life by optimizing the cleaning system. Dustcake weight or drag are better indicators of performance than pressure drop and should be used to develop an optimum baghouse operating protocol.     

重金属污染土壤植物修复及进展

土壤污染是当今面临的一个重要环境问题。常规的土壤污染物理化学治理技术 ,如客土换土法、冲洗法、热处理、固化、玻璃化、动电修复法等 ,由于其技术要求高或经济成本高昂 ,对土壤结构的扰动破坏较严重 ,因而 ,大规模推广应用存在较大问题。重金属超累积植物的不断发现 ,使人们认识到有可能利用植物于土壤污染的治理修复。自 2 0世纪 90年代起 ,植物修复成为环境污染治理研究领域的一个前沿性课题。研究表明 ,通过植物的吸收、挥发、根滤、稳定等作用 ,可以净化土壤或水体中金属污染物 ,达到净化环境的目的。近 10年来 ,在超累积植物的找寻培育、植物根际微生物共存体系研究、植物对重金属的耐忍性、超量吸收及其解毒机制以及植物修复的工艺技术方面已有不少研究 ,并取得长足的进展 ,现代分子生物学的发展以及基因工程技术的应用有可能使植物修复技术取得根本性的突破。     

Laboratory shake flask batch tests can predict field biodegradation of aniline in the Rhine

The aim of this study was to compare degradation rates of aniline in laboratory shake flask simulation tests with field rates in the river Rhine. The combined events of a low flow situation in the Rhine and residual aniline concentrations in the effluent from the BASF treatment plant in Ludwigshafen temporarily higher than normal, made it possible to monitor aniline at trace concentrations in the river water downstream the wastewater outlet by means of a sensitive GC headspace analytical method. Aniline was analyzed along a downstream gradient and the dilution along the gradient was calculated from measurements of conductivity, sulfate and a non-readily biodegradable substance, 1,4-dioxane. Compensating dilution, field first-order degradation rate constants downstream the discharge of BASF were estimated at 1.8 day⁻¹ for two different dates with water temperatures of 21.9 and 14.7 °C, respectively. This field rate estimate was compared with results from 38 laboratory shake flask batch tests with Rhine water which averaged 1.5 day⁻¹ at 15 °C and 2.0 day⁻¹ at 20 °C. These results indicate that laboratory shake flask batch tests with low concentrations of test substance can be good predictors of degradation rates in natural water bodies––at least as ascertained here for short duration tests with readily degradable compounds among which aniline is a commonly used reference.     

On the forming mechanism of the cleaning airflow of pulse-jet fabric filters

To reveal the formation mechanism of a pulse-jet airflow’s cleaning effect in a filter bag, a theoretical model is built by using the theory of the gas jet and unitary adiabatic flow according to given specifications and dimensions of the bags and resistance characteristics of the cloth and dust layer. It is about the relationship between cleaning system structure and operating parameters. The model follows the principle that the flow and kinetic energy of jet flow injected into a filter bag should be consistent with the flow of cleaning airflow in the bag and the pressure drop flowing through the filter cloth and dust layer. The purpose of the model is to achieve the peak pressure of cleaning airflow, which dominates the effect of the pulse-jet cleaning process. The cleaning system structure includes air pressure in the nozzle, structure and size of nozzle, exit velocity of nozzle, jet distance, and diameter of jet cross section. Based on the condition of the cleaning system structure and operating parameters established by using the theoretical model, Fluent software is applied to carry out a numerical simulation of the jet airflow field at the nozzle’s outlet, jet airflow field between nozzle and bag top, and cleaning airflow field in the filter bag. Experimental results are used to verify the reliability of the theoretical model. They are obtained in a pilot-scale test filter with a single bag, with length 2 m and in general full-scale dimensions of the cleaning system. The results show that when any rectification measure is not installed at the bag opening, the cross-sectional area covered by the jet gas is hardly sufficient to cover the entire area of the bag opening. A large portion of the gases injected into the filter bag will overflow reversely upward from the edge due to pressure differences between the upper area and lower area inside the bag opening. This led to a serious shortage of the cleaning airflow and ar limited increase in static pressure. When a venturi-type rectifier tube is installed at the bag opening, the jet flow is converted to funnel flow for which the cross-section velocity distribution is more uniform at the throat of the rectifier tube due to the guided effects of the upper tapered pipe. Then it is transited to stressful flow below the bag opening via rectified effects of the lower dilated pipe. The results show that the gap between the static pressure of gas in the bag and the expected value is significantly reduced. The theoretical value of the nozzle diameter is enlarged to compensate for two aspects of adverse effects of cleaning airflow and energy. This is because the flow is not a purely free-form jet from the nozzle to the entrance of the rectifier tube and because the gas suffers from local resistance while flowing through the rectifier tube. The numerical simulation and experiment show that the peak pressure of cleaning airflow in the filter bag is able to reach the expected value. The results confirm that the mechanism of the pulse-jet cleaning airflow and the calculation method of the pulse-jet cleaning system structure and operating parameters offered in this study are correct. The study results provide a scientific basis for designing the system of pulse-jet fabric filters.

Implications: Pulse-jet cleaned fabric filters are commonly used for air pollution control in many industries. Pulse-jet cleaning is widely used for this purpose as it enables frequent cleaning while the filter is operating. However, the theoretical system of the forming mechanism of the pulse-jet cleaning has not formed so far. This indicates the theoretical model plays an important role in designing effective pulse-jet cleaned fabric filters.     

应用于维生素C凝结水处理反渗透膜清洗策略

针对沈阳某药厂维生素C生产工艺中凝结水产量大、处理成本高和杂质复杂等问题,提出了采用反渗透技术对工艺凝结水进行处理。在前期确定的最优操作条件基础上持续运行,研究了运行临界通量、清洗时机和清洗方式等工艺条件。结果表明,在本工艺条件下,反渗透膜系统的临界通量介于1.1 L/(m2.min)到1.2 L/(m2.min)之间,斜率变点分析法确定的可逆膜污染周期为10 d;加强型清洗策略EFM(enhanced flux maintenance)的操作是针对不可逆膜污染的一种有效清洗方式,EFM持续30 min为宜,NaClO和NaOH都是有机污染的有效清洗剂,膜的平均恢复率分别为85.4%和81.6%,显示出实际应用的可行性,具有推广价值。     

Cloth media filtration and membrane microfiltration: serial operation.

A combined system comprised of a cloth media filter and a membrane microfilter operated in series was used to treat secondary effluent. The study objective was to investigate the effect of premembrane filtration on the maximum sustainable membrane flux, transmembrane pressure, and effluent quality. The maximum sustainable time-averaged flux under predefined operating conditions (i.e., 15-minute process cycle, 24-hour chemical cleaning cycle, and 30-day intensive cleaning cycle) was 127 L/m(2)x h. Typical flux rates for secondary effluent ranged from 40 to 55 L/m(2) x h. Effluent water quality from the combined system was high and independent of membrane flux and influent quality. Average membrane effluent water quality values were 0.04 NTU for turbidity and 1.4 mg/L for 5-day biochemical oxygen demand. Neither total nor fecal coliforms were detected. Based on the results presented herein, prefiltration would provide an annualized cost savings of approximately 12% over microfiltration alone for a 3.8 x 10(3) m(3)/d treatment facility.     

A review of biofouling and its control in membrane separation bioreactors.

Membrane separation technology is increasingly becoming an important innovation in biological wastewater treatment. Biofouling of the membrane is a major factor affecting the efficient and economic operation of membrane separation bioreactors (MBRs). This review summarizes the state-of-the-art progress in understanding the mechanisms and factors affecting membrane biofouling and the strategies for biofouling control. Biofouling mechanisms include the adsorption of soluble and suspended extracellular polymers on membrane surfaces and in membrane pores, the clogging of membrane pore structure by fine colloidal particles and cell debris, and the adhesion and deposition of sludge cake on membrane surfaces. Design and operating conditions of membrane modules and materials, hydrodynamic conditions in MBRs, process and environmental conditions of activated sludge systems, and the physicochemical properties of the wastewater are the dominant factors determining membrane biofouling. Current strategies to control biofouling include periodic relaxation, backwashing, chemical cleaning, and possible manipulation of hydrodynamic conditions and sludge properties. Achieving full integration of MBRs in wastewater treatment technology requires further research and development. Fundamental information on the bacteria, colloid, and membrane interaction, developed through multimethod and multiscale approaches, is particularly needed.     

A review of effects and control methods of particulate matter in animal indoor environments

This paper reviews the effects and control methods for particulate matter (PM) in animal indoor environments. PM in animal indoor environments represents a particular threat to the health of countless animals and millions of workers around the world. Because air in animal facilities has a higher portion of biological content than does air in other environments, the adverse health impact is much greater than it is for the same amount of PM in other environments. Source control, ventilation, and internal air cleaning can reduce PM concentration in animal indoor environments. Source control is typically the most economical method for PM control. Ventilation is the most widely applied technology, although uncertainties remain as to its effectiveness for PM control. Most internal air cleaners require frequent maintenance because of the high concentration and stickiness of PM in animal environments. Filtration is the most well-studied and widely used technology for internal air cleaning because of its low capital cost and high efficiency. Several trials using electrostatic precipitators have shown efficiencies of approximately 50% in removing PM concentration, but improvements are needed before they can be used widely. No report using wet collectors or centrifugals as internal air cleaners has been found.     

Irreversible fouling during multicycle microfiltration of wastewater effluent

This study focused on irreversible fouling during microfiltration of primary and secondary effluents from municipal wastewater treatment plants. Flow resistances were calculated from the sum of clean membrane resistances, resultant cake layer resistances, and consequent irreversible fouling resistances. Results from a dead-end cell experimental system showed that the accumulated cake resistance was dominating for microfiltration of primary/secondary effluents. Suspended solids in the primary and secondary effluents had a similar compressibility index, n, with a value of approximately 0.5, indicating that they were moderately compressible particles. The value of irreversible resistance is dependent on the intensity of membrane cleaning; however, for a given membrane cleaning strategy, this value steadily increased and reached a maximum after approximately 6 cycles of filtration and cleaning. This study provided an explanation for the significant drop of throughput flux in the early application of membrane processes, and a plateau flux approached correspondingly.     

Parameters governing permeate flux in an anaerobic membrane bioreactor treating low-strength municipal wastewaters: a literature review.

The objective of this review was to conduct a comprehensive literature survey to identify the parameters that govern the permeate flux in an anaerobic membrane bioreactor (AnMBR) treating municipal wastewater. Based on the survey, research to date indicates that the optimal membrane system for an AnMBR consists of an organic, hydrophilic, and negatively charged membrane with a pore size of approximately 0.1 microm. The use of both external and submerged membrane configurations shows promise. The operating parameters that affect permeate flux in an external membrane system are transmembrane pressure (TMP) and cross-flow velocity. The operating parameters that affect permeate flux in a submerged membrane system are TMP, sparging intensity, and duration of the relaxation period. Both cross-flow velocity and sparging intensity impart a significant amount of shear force on the biomass in an AnMBR. High shear forces can reduce the microbial activity in an AnMBR. In addition, high shear forces can reduce the size of the biosolids in the mixed liquor and increase the release of soluble microbial products. In this respect, external and submerged membrane systems are expected to perform differently because the magnitude of the shear forces to which the biomass is exposed in an external membrane system is significantly greater than that in a submerged system. The size of the biosolid particles and concentration of soluble microbial products in the mixed liquor affect permeate flux. Higher concentrations of soluble microbial products may be present in the mixed liquor when an AnMBR is operated at relatively low operating temperatures. Aerobic polishing following anaerobic treatment can potentially significantly reduce the concentration of some components of the soluble microbial products in the mixed liquor. It is not possible to remove the foulant layer on an organic membrane with caustic cleaning alone. Acidic cleaning or acidic cleaning followed by caustic cleaning is required to remove the foulant layer. This suggests that both biological/organic and inorganic material contribute to membrane fouling.