ICESP IX – Kruger National Park 2004

The International Conference on Electrostatic Precipitation (ICESP) is the official conference of the International Society for Electrostatic Precipitation (ISESP). The following is a list of papers from the IX ICESP Conference under their respective topic. Click on the papers title to view the complete paper in PDF format.

a 1-5 series – esp fundamentals (tuesday, may 18, 2004)
  • a01 efficiency of the precipitation of fine particles influenced by the esp supply mode.
    • Behaviour of fine particles is still a “hot topic”, especially, because of the regulations connecting to PM 2.5. To determine the performance of ESP for fractions 2.5 μm and below is extremely important, because these particles are more dangerous for the human health than larger pollutants.The present examinations represent further development of our previous ESP model [1,2,3] especially by taking into consideration the change of the supply mode (different types of the time function of the supply voltage and supply current) of the electrostatic precipitators. As a case study, two different supply modes are compared, continuous DC case and supply by impulse voltage.
  • a02 enhanced corona discharge using innovative rigid discharge electrodes (rde).
    • The collector efficiency of an ESP is directly related to the applied corona power. However, this corona power needs to be applied effectively in order to impart the largest benefit possible at the actual point of corona discharge which emanates from an element referred to as a discharge electrode.Discharge electrodes have evolved quite ungrammatically over the years and it is still quite common today to be faced with ESPs equipped with such elements which were designed and installed over 30 years ago. However, new demands for higher efficiencies coupled with corresponding lower maintenance costs, have led to some manufacturers favouring technologies and applications more suitable for today’s general usage. This implies looking into models which consider not only updated technology aspects but also manufacturing process, reliability in the long term as well as easy installation in order to effect cost effective replacements.Rigid Discharge Electrode (RDE) technology has been utilised extensively in Europe and North America and it has been found that the electrical characteristics of such electrodes have contributed significantly to an improvement in the efficiency of many ESPs. Furthermore, because of greater flexibility in geometry and configuration of the electrode units, RDE technology allows for such improvements as increases in Specific Collection Area (SCA), aspect ratio, migration velocity and treatment time.This paper deals with an innovative type of RDE conceptualised in South Africa, considered specifically to optimise the practical issues associated with effective corona discharge processes and at the same time improve the expected life cycle of such devices combined with a simple configuration providing for easy replacement of obsolete or faulty units.
  • a03 improvement of fine particles collection efficiency in large pulverized coal power plants. esps retrofitting to hybrid collectors.
    • The last European directive (2001/80/EEC) for Large Combustion Plants limits the emission of particulate matter in E.U. to 50 mg/Nm3 for ≥ 500 MWth existing coal power plants and to 30 mg/Nm3 for ≥ 100 MWth new facilities. In other hand, it is probable that next European regulations will limit the fractions more difficult to collect: PM10 and PM2.5. These limits can be difficult to reach considering only existing ESPs, particularly for some high resistivity ashes.In this sense, this paper describes a series of pilot plant tests carried out in order to enhance the ESP efficiency and to prove the new emergent hybrid collector (HyColl) technology applied to flue gases from coal power plants. The ESP tests have been performed with the main objective of studying ESP behaviour when different coals and different filter configurations/energisation methods are used. The primary aim of this study was to reach conclusions about the ESP design and sizing optimisation for high efficiency applications. In the other hand, the HyColl tests have been performed with the objective of comparing the efficiency and costs of this new technology with ESP technology.A HyColl consists of an ESP followed by a fabric filter (FF) installed in the same casing. The tests have been carried out in an ESP/HyColl pilot plant developed within the HyColl Project (ECSC 7220-PR/079). The pilot plant consists of an ESP with three electric fields followed by a 32 bags FF section, processing 15,000 Nm3 of real flue gases extracted from the flue gas ducts of a power station. The pilot plant is located at Los Barrios P.S. (Spain), but additional evaluation tests have been performed at Dürnhror P.S. (Austria).Modifications on design and operation parameters of ESP and HyColl have been tested according to the factorial design of experiments in order to obtain their optimisation for collecting particulate matter in coal combustion flow gases.
  • a04 the influence of the discharge electrode shape on the efficiency of electrostatic precipitator.
    • The objective of this experimental study was to investigate the influence of corona electrode design on the collection efficiency. The experiments were carried out with fly ash from lignite combustion in a pulverised-fuel boiler and a fluidized-bed boiler, and with three corona electrodes which differed in design. Current-voltage characteristics and collection efficiency curves were established. The study was performed under laboratory conditions with a horizontal electrostatic precipitator model. The chamber of the experimental setup had a length of 1000 mm, a height of 450 mm and an interelectrode spacing of 400 mm. The results (gathered in tables and plotted in figures) show how the design of the corona electrode and the type of the fly ash affect the collection efficiency under experimental conditions. This finding implies that the optimization of the corona electrode design should include not only the parameters of the electric field, but the physicochemical properties of the fly ash as well.
  • a05 turbulence studies of negative corona esp.
    • This investigation presents experimental velocity fields obtained by stereo particle image velocimetry (stereo-PIV) for 3 different pin-electrodes in a laboratory model of a negative corona ESP at low particle loads. Additional data include photographic records of dust patterns, measured distributions of current density and particle size distributions upstream and downstream of the 0.2×0.2 m by 1.0 m long, seven-electrode test section, yielding experimental efficiencies. A computational study of velocity and concentration fields for one type of electrode show encouraging agreement with experiments. Pin electrodes yielding less well-organized secondary flows tend to have higher efficiency, even though the turbulence level is higher.More specific topics include measured particle fluxes close to the collector plate, which suggest considerably higher effective drift velocities than those predicted and normally used in the laminar sublayer as boundary condition for concentration fields. Using the measured velocities gives good agreement experimental efficiency. A hypothesis is advanced to explain the differences. Also, the source of turbulence generation is discussed in light of current theories and the present experimental data, which provide estimates of shear production. The possible coupling between fluctuations in electric field variables and gas velocity has been studied experimentally by measuring velocity-current correlations near the collector plate, which yields a production comparable to that due to shear flow.
a 6-10 series – esp fundamentals (tuesday, may 18, 2004)
  • a06 precipitation of fine particles considering uncertain dust properties
    • It is well-known, that dust properties have a strong influence on the process of the precipitation. Some of the main relationships between the precipitation efficiency and the parameters of dust, like specific resistance, permittivity, particle size etc. have also been published [1].There are several uncertainties in the determination of these parameters. Some parameters can not be properly determined, some properties cannot be measured continuously, and some of them are changing during the operation of ESP, etc. Because of the uncertainty of these factors the reliability of ESP models can decrease with decreasing accuracy of the input data.The most important aim of our investigations was to determine the effect of the variation of the dust parameters on the precipitation. The degrees of these dependencies have been investigated and presented in the paper. Based on the new results, it is possible to estimate what accuracy is necessary in case of different parameters to obtain reliable ESP models.
  • a07 static and dynamic back-corona characteristics.
    • Voltage-current characteristics are a basic tool to analyse the operational conditions of an electrostatic precipitator, and to detect the onset of Back-corona, that strongly affects the collection performances. In this investigation, a laboratory set-up has been arranged, with a classical ESP wireplate configuration; both static and dynamic voltage-current characteristics have been measured and analysed with different geometries, dust characteristics, and layer thickness. Similar results have been also obtained in an industrial ESP, and compared with the laboratory results.In the laboratory ESP, the static voltage-current characteristics and the collection efficiency have been measured as functions of time; with high resistivity dust, back-corona takes place as layer thickness increase, with a decrease of the efficiency and a sharp raise of the current. The effect of electrode type and powder resistivity has been analysed. With varying applied voltages, the dynamic voltage-current characteristics show an hysteresis cycle, the recorded values depending on the slope of the applied waveform. The shape of the dynamic characteristics changes significantly with the onset of back-corona.A self-consistent numerical model has been applied to simulate static and dynamic voltagecurrent characteristics in absence of back-corona. These simulations allowed to analyse the retarding effects of the different physical process (capacitive charging, ion drift, space charge movements), and to estimate the corresponding time constants. Finally, the dynamic effects of back-corona have been analysed.A second set of experiments have been realized in a 600MW power plant: ESP static and dynamic characteristics have been measured with fly ash of low and high resistivity: the results are very similar to those obtained in the laboratory ESP, and confirm that it is possible to define a specific “signature”, on both static and dynamic V-I characteristics, of the different physical processes associated to the particle captation, including back-corona.
  • a08 study on charging particles of the magnet enhancement corona discharges.
    • In this paper, the characteristics of the magnet enhancement corona discharges and their function for charging particles are introduced. The experimental results demonstrated that the magnet field could obviously increase the discharge current and enhance the particle agglomeration in corona discharges. The deflection of free electrons between the discharge and collection electrodes was measured. Therefore we can deduce that both the energy of free electrons and the concentration of free electrons and ions are increased in the magnet enhancement corona discharges. Comparing with the uniform magnet field, the uneven magnet field formed by the permanent magnet nearby the discharge electrodes can more effectively intensify corona discharges. We developed an aerosol charger of the magnet enhancement corona discharges with permanent magnet. The charging current was increased by 25% in a magnet field of 0.02T.
  • a09 trials and tribulations of an esp systems engineer – back to basics at matimba
    • Emission excursions are sometimes explained by weird and wonderful theories and speculations about changes in ash chemistry and a whole host of other often complex reasons. In many instances when this happens one finds that surprisingly often the “basics” have been overlooked. In extreme cases this could be something as obvious as a field being out of service. This Paper addresses the basics.Matimba Power Station is situated in an environmentally pristine area in the northern part of South Africa, 13 km west of Lephalale in the Limpopo Province approximately 75 km from the Botswana border. This area is known for its “eco-tourism” and local environmentally conscious communities do not easily accept this Power Station and other industries associated with the abundant coal reserves found in the area. The long-suffering ESP Systems Engineer often has to bear the brunt of these conflicts of interests.
  • a10 acoustic horn made electrostatic precipitator collecting plate and hopper clean in zhangjiakou power plant.
    • The two 4-fields, 230 m2 flow area, magnetic hammer top rapping precipitators of a 300MW unit in Zhangjiakou Power Plant encountered dust accumulation and clogging difficulties, especially in third and fourth fields. By mounting acoustic horns of SQ-75 type, produced by Liaoning zhongxin Automatic Instruments Company, for one channel, four fields on the top, in the sidewalk between electric fields and in the hopper, dust scale up and accumulation problems were eliminated. Operation voltage and current were increased by 6% and 28% respectively. Working principle and detailed description are given.
a 11-15 series – esp fundamentals (wednesday, may 19, 2004)
  • a11 electrostatic precipitator enhancement by online monitoring of collecting electrode mass.
    • South Africa’s Eskom is the African continent’s largest electricity Utility, generating 98% of South Africa’s electricity needs and 60% of Africa’s needs. It currently burns in excess of 100 million tons of coal annually and this is more than any other single Utility. Electrostatic precipitators (ESP’s) remain the primary device used for gas cleaning to clean 75% of this coal.Eskom has now more widely applied the research lessons in the practical use of loadcells as a means of enhancing electrostatic performance by continuous real-time mass measurement of the collecting electrodes (CE’s). A previous paper presented at ICESP VIII detailed this work at Eskom’s Lethabo power station and its effectiveness in optimising plant operation. This paper will describe the continuation of this work at another Power Plant and focus on real-time, in-situ measurements.The technology has been implemented on a single casing at Eskom’s 3 000 MW Kriel Power Plant as part of its upgrade and refurbishment program. This paper will detail this work and present measured results from both before and after the refurbishment. Other ESP operational CE patterns, will be also be presented with the aim to providing further insight into ESP operational behaviour.
  • a12 precipitator emission management – the wider perspective.
    • An integrated approach must be taken to achieve the best possible precipitator performance, rather than addressing each aspect in isolation. This requires the collection of a significant amount of data before the implementation of an emission management strategy to coordinate all areas of influence.To allow an integrated approach it is necessary to install a Precipitator Process Management Systems (PMS) also referred to as Air Emission Management Systems (AEMS).Assuming that the precipitator itself is in sound mechanical condition with acceptable gas distribution and rapping, the integrated approach can only take place after the collection and detailed analysis of process and electrical data. Trending of process and energisation parameters is used as the base data for the management strategy.An acceptable decrease in emissions has already been achieved at Eskom Matimba Power Station as a result of improved mechanical integrity and better electrical energisation (see the previous presentation “Trials and tribulations of an ESP Systems Engineer – Back to basics at Matimba”).

      This presentation describes the operation of a PMS subsequently installed at Matimba during 1999– 2000 and the further improvement in emissions achieved as a result.

  • a13 centralized control and monitoring of multiple esps in power station
    • The increasing concern for the environment and consequent stringent norms for air quality from thermal power plant emissions, have resulted in a greater demand on the performance of ESP. ESP being a down stream equipment is affected by various boiler parameters, requires close control and monitoring. This has resulted in the development and deployment of microprocessor based controllers for high voltage energisation and for rapping functions. For total control of ESP in a co-ordinated manner, often PC based or similar integrated control systems are used.Such a PC based system is designed for single point operation of ESP of a boiler. It integrates control and monitoring function of all sub-controllers like ESP energisation controller & rapper controller. As a co-ordinated controller, it is able to manage the total ESP operation like adjustment of rapper timings depending on field availability or boiler load. It also optimises the energisation of all fields in an ESP and improves the rapping performance by bringing down the current in the rapped field.In a power plant complex, there may be a number of boiler units, spread out over a larger area. This often calls for viewing or controlling the ESPs of all boiler units from a single location for analysis. Towards achieving this, a centralized controller for multiple PC based control systems was developed.The centralized controller is a PC based system developed on Windows platform. All the PC based integrated control systems of all boiler units in a plant are connected to centralized controller through RS-485 over MODBUS protocol. Any parameter from any ESP can be monitored and controlled from the centralized controller.

      This paper discusses the philosophy and implementation of centralized controller.

  • a14 performance enhancements achieved with high frequency switch mode power supplies
    • For over 40 years the most commonly used device to power electrostatic precipitators were standard 50/60 Hz SCR Controller and Transformer/Rectifier sets. However, in the last 4 years a new Power Supply has been introduced to the ESP industry. This Power supply is based on High Frequency Switchmode technology. The new Switchmode Power Supplies are capable of dramatically different performance than the older, 50/60-hertz linear transformer/rectifier sets.Recent comparative tests of the two technologies were performed in the USA at Southern Company’s Savanna electric Plant Kraft 163 MW unit number 3. During a rebuild of the ESP on this unit, in the spring of 2002, standard 50/60 Hz transformer were installed on the east ESP casing and Switchmode Power Supplies were installed on the west casing. This modification also resulted in plate spacing change from 9” to 11.25” with ridged electrodes and a SCA of 322 ft2/1000 acfm. This paper will discuss the performance enhancements seen with the Switchmode Power Supply during testing conducted between the two sides using US EPA Method 17 particulate testing.
  • a15 the development of an algorithm for the dynamic adjustment of pulse repetition frequency for minimizing back corona in electrostatic precipitators.
    • Within the ESP industry, power supply synchronous pulsing is a well known method of dealing with Back Corona resulting from the precipitation of high resistivity particles. Often, especially in the case of moderate Back Corona, or on a stable process, a set-up once and forget method of adjusting the controllers is satisfactory. In these circumstances, the time taken and skill level required to establish the initial settings is not an important factor.Under extreme conditions of Back Corona, or with an unstable process, this approach is not viable. Automated optimization algorithms were developed and run at regular intervals in order to establish and update the controller settings.The paper describes the development of a dynamic algorithm which having established the optimum pulse repetition frequency, attempts to further optimize on-the-fly in order to compensate for short term changes in the operating conditions.It is understood that this type of control algorithm is often required to be retro-fitted in older plants where these types of problems are already known to exist. The paper takes a practical approach to this in considering how to deal with less than perfect voltage divider signals when utilizing existing T/R sets for example.
a 16-20 series – esp fundamentals (wednesday, may 19, 2004)
  • a16 orchidee: efficiency optimization of coal ash collection in electrostatic precipitators.
    • In a coal thermal power plant, one of the industrial solutions for collecting the fly ashes produced during the combustion process, is the electrostatic precipitation. However, electrostatic precipitation is a process affected by many parameters, in particular the physical and chemical nature of the ash, the flow rate and composition of the flue gas. In addition, the operation and the maintenance of an electrostatic precipitator may prove to be difficult on account of the great number of physical processes concerned.To satisfy current regulations, the efficiency of the electrostatic precipitator must always be greater than 99.5%. To sustain these high performances requires good control of the impact of various malfunctions on the level of emissions. For that, two distinct approaches can be described. The first, influenced by the problems the ESP manufacturers, describes the process as a whole and requires a substantial experimental database. The second, influenced by research in universities, accurately describes the physical phenomena.With the ORCHIDEE software, an intermediate approach is proposed, based on physical modelling of the collection process. This approach enables to estimate the efficiency of an electrostatic precipitator without using an experimental database, and to be independent on manufacturer’s empirical data. The operator is then able to have a better real time understanding of the problems, and to react efficiently. By introducing properly all input data, ORCHIDEE makes it possible:- to evaluate the impact of combustion parameters on dust emission rapidly (too much air inleakages, flue gas temperature too high in the electrostatic precipitator).
      – to test the hypotheses of blending types of coal to avoid back-corona.
      – to evaluate the impact of unfavourable distribution of the flue gas in the electrostatic precipitator.
      – to simulate electrical malfunctions: a field or section out of service.

      The Maintenance Department can optimise its actions. The Technical Department can make a better assessment of slow drift in operation. The Engineering Department can better appreciate actions for renovation, as the ORCHIDEE physical model makes possible to verify the effect of changes in internal components (height, plate-to-plate distance, and type of wires), changes in the electrical power supplies, the addition of a new field, for both existing units to be retrofitted, and for new units that to be designed.

      ORCHIDEE is a tool to assist operation and maintenance of electrostatic filters, that is unique for its high scientific content and its user-friendly interface: it has shown to fulfil the expectations of its users.

  • a17 improvements of an european type electrostatic precipitator with chinese design experiences
    • In the beginning of 1980’s, China imported precipitator technology from a European country. Several hundreds of such type precipitators have been manufactured and operated in Chinese cement and other industries. Some drawbacks of detailed design lead to abnormal operations. Improvements by using of Chinese experiences are described.
  • a19 practical experience and results of esp operation collecting high resistivity fly ash with high dust load.
    • The article describes results gained during an ESP replacement programme at Aksu power plant in Kazakhstan, carried by the power plant and under the pressure from the State, in order to improve environmental situation in the region.The task was to both meet reduced emission requirements when collecting a high resistivity fly ash from Ekibastus coal in combination with the use of the same foundation and support structures. The coal has low sulphur (<0.6%) and high ash content (> 40%) resulting in an ESP inlet load of 60 g/Nm3 and higher. Intensive back-corona was expected to develop inside the ESP. The fly ash is highly abrasive. The combination of these factors required special precautions during project implementation.Combination of modern ESP technology with the use of spiral discharge electrodes and state-ofthe- art microprocessor controllers resulted in successful project implementation with much lower than required emission level.
  • a20 how to eliminate esp insulator thermal break down and insulation aging.
    • High voltage electric field combining with high temperature may lead to ESP insulator failure. Particulates having a relatively lower breakdown voltage strength stick on the insulator surface can induce corona discharge and local temperature rise thereby speed insulator aging. Select insulator material with higher Te (the temperature when the resistivity lowers to 1MΩ·cm) and optimize design to even the field around insulator can effectively protect insulator from heat breakdown and aging.
a 21-25 series – esp fundamentals (thursday, may 20, 2004)
  • a21 esp emission reductions with advanced electrode rapping together with novel energizing methods.
    • To help keep the collecting plates clean, Power Down Rapping (PDR) and Power Off Rapping (POR) have been used for many years.In this paper it is shown, that the simple TR interaction available with PDR and POR can be made in more elaborate ways, and that this greatly reduces the ESP emission compared to the old strategies. Increased rapping losses that may cause major emission peaks when conventional PDR or POR is used can, in many cases, be managed with the more advanced rapping regimes discussed in this paper.For the ESP entry fields, excessive dust build-up on the collecting plates may increase the voltage that is required to start the corona. The increased voltage increases the risk for spark-over limitation at a [too] low current.

      This and other disturbances have been successfully addressed with more intricate novel rapping strategies combined with new ways of using PDR, what we call Power Control Rapping (PCR).

      Compared with ESPs that use conventional rapping the novel methods have in several ESP plants reduced the emission with 30 % for low to medium resistivity dusts. For dusts characterised by a high resistivity this novel method is even more successful, and emission reductions of more than 50 % have been obtained at several plants.

      Combining advanced rapping and a more smooth HVDC supply – also referred to as Switched Mode Power Supply (SMPS) technology – even higher emission reductions have been obtained in a number of ESPs, especially when operating with low to medium resistivity dust.

      It seems possible that the above mentioned emission reductions can be obtained for all ESPs, provided the dust is, for whatever reason, difficult to dislodge from the collecting plates.

  • a22 cfd simulation of gas flow and particle movement in esps.
    • A first step in order to model the electro-hydrodynamic flow inside a full Electrostatic Precipitator (ESPs) is to consider the gas distribution separately. Flow management by gas distribution screens are needed in the inlet and outlet funnels and perhaps also between sections of different electrical fields. Currently, the traditional approach of cut-and-try in the design phase and physical scale model or field tests in the order executing phase is being replaced by Computational Fluid Dynamics (CFD) at FLS Airtech.The distribution of three-dimensional flow and pressure are simulated by a commercial CFD code giving accurate and highly detailed information over the calculated domain. Furthermore, the code includes a specially designed FLS Airtech module for modelling the effect of the gas distribution screens.The paper presents simulations of full ESPs including inlet funnel with gas distribution screens, precipitation sections with collector curtains and anti-sneakage baffles, hoppers with partition plates and outlet funnel with gas distribution screen.

      Attention is paid to different inlet/outlet funnels, advantages of screens between sections of different electrical fields and on anti-sneakage baffles. Further, numerical simulations versus full scale and model scale measurements are discussed. The study of different inlet types demonstrates the flexibility of the FLS Airtech ESP design making it easy to implement depending on layout limitations or process conditions. Moreover, calculations with small particles indicate that sneakage is an important issue and implementation of anti-sneakage baffles can reduce emission significantly.

  • a23 solution and analysis on three dimensional math model of dust concentration distribution in esp.
    • Solutions of the three-dimensional mathematical model on particles sedimentation in ESP were deduced, as well as the precipitation efficiency formula. Comparisons were given between onedimensional mathematical model and twodimensional mathematical model. According to the experimental results, the discussions on the concentration distribution were carried through. All of these can describe the movement of electrified particles in ESP more correctly, so as to supplying the corresponding reference base for the design, manufacture, operation and precipitating efficiency forecast of ESP.
  • a24 simulation of particle transport in electrostatic precipitators.
    • Simulation models for sizing of ElectroStatic Precipitators (ESPs) have been developed for the last 15 to 20 years, but only a few models take into account all physical processes involved, i.e. electric field, particle space charge, dust resistivity, particle concentration field, and flow field, and most models are confined to two dimensions.A new extended FLS-Airtech-model simulates most physical processes in an ESP and is fully threedimensional. The model has been implemented in a commercial Computational Fluid Dynamics (CFD) code in order to obtain a high degree of flexibility and generality and an efficient visualization tool for the model output data.The presented results include validation of the extended model against pilot and full scale ESP data. Further, simulations based on a typical FLS Airtech ESP geometry with spike discharge electrodes are presented. Focus is on model results and on discussions of different parameters important for optimal operation of ESPs, e.g. current density, secondary flows, turbulence, particle characteristics and charging. Most of these parameters are difficult or even impossible to measure in full scale or even in pilot ESPs.
  • a25 demystifying the rating plate of t/r sets.
    • When working with retrofit projects some data for the T/R set that is not possible to find on the rating plate is often needed. Sometimes the rated voltage is indicated in a way that it can be interpreted wrongly. This leads often to mistakes and time wasting. In other cases, e.g. by operational problems, the performance of the T/R set needs to be assessed and again, the ESP manufacturer needs the relevant information.Because of the lack of uniformity among T/R set manufacturers in marking their product, this paper explains the type of electrical information that should be indicated on the rating plate as a minimum requirement. The reason for that is illustrated with different examples, where the T/R set operates with different loads.
a 26-30 series – esp fundamentals (friday, may 21, 2004)
  • a26 improved control of primary fine particulate emissions with electrostatically stimulated fabric filtration.
    • Southern Research Institute (SRI), under a cooperative agreement with the United States Environmental Protection Agency (USEPA), is reporting the results of an investigation of electrostatically stimulated fabric filtration (ESFF) for particulate control on a utility boiler fired with pulverized coal (2001-2003). In pilotscale testing at the SRI Combustion Research Facility and in a long-term, pilot-scale demonstration of ESFF at a full-scale utility boiler, ESFF consistently outperformed conventional fabric filters (2001-2002). For these tests particle charging was accomplished with high voltage electrodes mounted outside of, but co-axially, with the pulsejet filter bags. With ESFF, total mass emissions without cleaning were one-fourth to one-fifth of those for a conventional pulse-jet fabric filter (FF). Penetration of particles smaller than one micrometer was about one order of magnitude less with ESFF. In addition, pressure drop increased about one-third as fast with ESFF as compared with FF, reducing the frequency of bag cleaning. Since a significant fraction of the total particulate emissions occur as a consequence of cleaning, the reduced cleaning schedule in itself leads to lower emissions of all particle sizes. Recently, additional testing (2003) has been completed using a cooled-pipe precharger to impart charge to the fly ash particles. The previous high voltage electrodes were replaced with large diameter electrodes intended to produce only a collection field. Improved baghouse performance was observed with this arrangement, producing filter drag values 50 to 60% lower than those experienced during normal baghouse operation. Of special note was the observation that significant performance improvement was measured with only the collection field energized (no precharging of the fly ash).
  • a27 electrostatic precipitators, bag filters and emission standards for coal-fired power plants in china.
    • From 1980 to 2003, power installed capacity in China grown from 65,869 MW to 384,500 MW, near 6-foldes increased. By the end of 2003, coal-fired power increased to 285,640 MW, thus induced continuosly increased air pollutions. Accompanying the emission standards from tolerant to stringent, high efficiency dust collectors gradually played dominative role. From 1955, precipitators went into Chinese power plant and by 2003 it already shared 82% of the total coal power capacity. For precipitators, very difficult coals and rather favorable coals were encountered. In 2001, first “successful” bag filter put into operation, after that, it grown very rapidely. From January 2004, new coal power emission standard of 50mg/m3 implements, considering the big variety of Chinese coal, the choose between precipitator or bag filter will be worth considering. An primary economic coparison is given.
  • a29 s03 injector fouling in flue gas conditioning systems.
    • SO3 injection probe fouling is a major concern in the operation and maintenance of SO3 flue gas fly ash conditioning systems. The source of the problem is moisture in the combustion air used by the sulfur burning SO3 gas generator systems. Proper SO3 injector probe operating temperature control and operation can alleviate many of the problems. The use of dry combustion air in combination with conventional SO3 flue gas conditioning systems has the potential of reducing both the quantity of sulfuric acid generated and the dew point temperature of the sulfuric acid mist formed in the hot gas piping and SO3 injection probes. The advantages of dry combustion air will be in reduced injector fouling – resulting in lower maintenance costs and improved fly ash conditioning performance. The lower sulfuric acid dew point temperature of the SO3 gas will offset the additional operating costs associated with producing the dry combustion air and can also reduce the capital costs for new installations when combined with SO3 gas flow splitting and biasing technology.
  • a30 flue gas conditioning – so3 injection rates for south african coal ashes
    • Flue gas conditioning at some Eskom power stations has required lower SO3 injection rates than those predicted by models or FGC vendor experience. The required injection rates were about a third of predicted, which was an unexplained anomaly. The paper offers an explanation and proposes a method for determining whether a coal ash will behave “conventionally” with SO3 FGC or will require a lower than expected injection rate.
a 31-32 series – esp fundamentals (friday, may 21, 2004)
  • a31 the newest technical results capable of remarkably increasing esp efficiency.
  • a32 optimization of existing esp’s represented by an example.
    • This paper describes the process of optimizing an existing electrostatic precipitator unit fitted to a coalfired boiler. Specially, there was a unit selected whose remaining service life had been extended by 15 years, and whose electrostatic precipitators (ESP) came from different manufacturers. Furthermore different types of coal had been used during the boiler’s service life, making repeatedly changing the demands on the electrostatic precipitator unit.
  • a33 influence of corona quenching on charging and collection of nanoparticles
    • The increasing importance of nanoparticles regarding health aspects and new nanoaerosol production processes requires the adoption of reliable particle collection techniques. In these fields, electrostatic precipitation is an economically promising technique. With respect to nanoaerosol processes electrostatic precipitation might be a cost effective competitor to the surface filtration technique – the current state of the art. Due to the demand of economic mass throughputs an efficient application of electrostatic precipitators can be limited by corona quenching phenomena, which are induced by the necessarily high particle concentrations.In this work three issues are addressed: First, the precipitation of two particle systems with diameters below 100 nm within a one-stage lab-scale wire-tube ESP is studied experimentally and theoretically. Whereas the first particle system, spherical DEHS-particles, was chosen because of the ideal particle shape, a SiO2-system was investigated because of it’s technical relevance as a system of agglomerate structures. The second aspect focuses on the charging behaviour of these particle systems. Finally, the third case deals with the influence of the aerosol concentration on both the precipitation and the charging behaviour, respectively. For that purpose, the used SiO2-aerosol generator allows for a variation of particle concentration over two orders of magnitude up to some 108 #/cm3.A Deutsch-similar correlation between measured overall collection efficiencies and migration velocities is found, covering all investigated cases: negative and positive corona, spherical and non-spherical particles, different particle sizes and – what might be the most important result – both low and high corona quenching conditions, respectively. It is shown for the given case of electrostatic precipitation of nanoparticles that the particle movement happens to be independent on the charging circumstances. The precipitation correlates only to the charging result (electric particle mobility) in the average electric field, represented by the migration velocity or the non-dimensional Deutsch number.

      Since the charging physics for particles below 200 nm is dominated by the diffusion charging mechanism, the established Fuchs theory (1963) is used for the comparison with the measured charge values, with ion density calculations based on an analytical solution of the Poisson equation. In the case of negatively charged particles for high N·t-products a considerable underestimation of the experimental data is observed. In the case of positively charged particles the measured data match the predictions better, but for N·t > 1014 s/cm3 the measured values also tend to surpass the predicted ones.

  • a34 does so3 flue gas conditioning have an impact on the environment – an assessment
    • The impact of SO3 flue gas conditioning on the environment has been a topic that has not received a lot of attention in the past. This is mainly due to the huge improvements in ESP performance that can be achieved by the utilisation of this technology. The amount of SO3 being injected only forms between 2% and 4% of the total SOx (total SO2 and SO3) concentration and it was accepted that all the SO3 reacted with the fly ash in order to achieve the improved ESP performance. SO3 FGC is a very effective way of reducing the particulate emissions and has been effective in doing so at all the Eskom Power Stations where it has been implemented. There are however some exceptions where SO3 FGC alone will not be able to achieve the low emission levels that will be required by the Chief Air Pollution Control Officer (CAPCO). These are typically the older power stations with small ESP’s that have been sized to achieve the emission required at the time of construction and are not acceptable for current requirements. These power stations normally have to install SO3 FGC and upgrade their existing ESP’s to be capable of reliably giving emissions below 50mg.S.m3 or they have to install fabric filters. SO3 FGC forms an integral part of Eskom’s drive in the reduction the particulate emissions and it was therefore decided to evaluate its impact as part of the Eskom Emissions Research Portfolio. This paper reports on the results obtained during this assessment.
b 1-3 series – esp applications (tuesday, may 18, 2004)
  • b01 retrofit of scr -systems – formation mechanisms of so3- aerosols and implications on the flue gas cleaning system.
    • The retrofit of DeNOx-systems has been accomplished in nearly all German power plants during the nineteen-eighties as an implementation of the respective prescriptions of the environmental legislation (13. BImSchV). Since then, many years of experience have been accumulated at E.ON Engineering regarding the operation, the efficiency and the impact on the total flue gas cleaning system. Especially the often-reported opacity problems occurring after the retrofit of DeNOx-systems still remain to be an issue of key-interest.This paper shall contribute to the general understanding of formation mechanisms of SO3 in its different states, its concentration profiles along the flue gas path and the specific effects related to SO3 or sulphuric acid observed in the individual components of the boiler and flue gas cleaning system. Results obtained in several measuring campaigns in power stations in Germany as well as in the United States are shown and discussed. The dependencies on specific process conditions such as sulphur content of coal, the catalyst type, air heater setpoint temperatures and the general configuration of the plant are discussed.

      As sulphuric acid as a conditioning agent has an important effect also on the efficiency of electrostatic precipitators, the relevant test results are specifically reviewed in this respect.

  • b02 experiences of wet type electrostatic precipitator successfully applied for so3 mist removal in boilers using high sulfur content fuel .
    • In thermal power plants, especially using high sulfur content fuel, much attention is recently paid to SO3 emission, because gaseous SO3 in flue gas is condensed to sulfuric acid mist (SO3 mist) in the wet type FGD, which is installed to meet SO2 emission regulation. SO3 mist is very fine under-sub-micron sized particulate matter (PM), which is very visible even if the concentration is relatively low, and causes air pollution. SO3 is often recognized as a part of the total SOx. However, recently, discussion comes out, especially in the United States, that the condensed SO3 mist should be included in the total dust instead of SOx and regulated together with solid dust. In order to remove SO3 mist from flue gas, wet type electrostatic precipitator (WESP) installed in the horizontal gas flow at downstream of FGD (Flue Gas Desulfurization System) is one of the best solutions and the most proven technology at this moment. This paper describes the experiences of WESP successfully applied in Japan and Europe, and also shows the advantages of the technology. Measuring method of solid dust and SO3 concentration is a very important issue for WESP application, which is discussed in this paper as well.
  • b03 electrostatically augmented granular gas filters: a solution in search of a problem?
b 4-9 series – esp applications (tuesday, may 19, 2004)
  • b04 on the choice of esp design for a multitude of world low sulphur coals.
    • Electrostatic Precipitators (ESP’s) are the main particulate collectors for most new power stations firing coal. ESP’s are able to achieve present emission regulations and are often preferred by users due to robustness, low operating cost and high availability. Many new boilers will burn low sulphur coal. Present legislation requires limits on sulphur emissions and with the burning of low sulphur coal it is then often possible to avoid desulphurisation equipment.The owner of the plant wants to have the flexibility to buy any coal on the world market for various reasons. Coals with sulphur content less than 1% and relatively low ash content are readily available and are exported from countries like Australia, South Africa, Indonesia, China and Latin America. The ash properties from such coals vary widely and the impact on the ESP size can be dramatic. Coal and coal ash analyses in combination with boiler conditions, humidity, gas temperature etc. are considered when selecting the size and design. The specification for the ESP often comprises a wide selection of coals that might be fired several years later. What is a realistic size of the ESP taking the specific coals or the ranges into account?

      The paper discusses the influence from various parameters on the ESP size and suggests different strategies to be applied in order arrive at cost-efficient solutions. It is important that the boiler vendor has close contact with the ESP vendor to optimise the whole plant. Furthermore, the plant owner should have a proper knowledge of limitations and possibilities when buying the ESP.

  • b05 investigations on fly ash resistivity of varieties of coals used in indian power plants.
    • Fly ash resistivity measurements facility has been set up at Centre for Energy studies, Indian Institute of Technology Delhi (India) to develop a data base for India and to monitor the impacts of any technique use to modify ash resistivity, like U.S. laboratories we also follow the IEEE Standards Criteria (IEEE Std. 548- 1984) and guidelines for the laboratory measurements and reporting of fly ash resistivity. The test procedures captures the changes in ash resistivity with respect to temperature and composition changes of ash. The required instruments needed are Kiethly electrometre, Fluke power supply, Blue M oven, lattice frame, digital temperature readers, variacs, vacuum equipments, relay rack and sensitive thermocouples.In the present study we have measured the fly ash resistivity and its variation in ascending and descending temperature modes (90-460 0C) for the fly ash samples of different thermal power plants. The study also reports the results on the effect of sodium conditioning in coal on fly ash resistivity and it is observed that the resistivity decreases significantly due to change in the chemical composition of the coal.
  • b06 retrofitting pollution control equipment in indian power plants and other industries to meet the present more stringent norms.
    • Electrical energy produced in any country is one of the measures of the development taking place in that country. The energy produced is mainly based on the resources available such as water flow, coal, oil, gas, nuclear fuels etc. The richness of coal in India prompted the Power Plant Planners to install Thermal Power Stations. During the pre-independence and post independence era in early 50s, the need was to generate power and hence much attention was not paid to the Pollution aspect and this continued upto late 70s. The awareness created on the Pollution effect on the Society and the enormous amount of erosion subjected to the equipment forced the authorities to make the pollution norms more stringent. This compelling norms which came into existence in 80s necessitated the Power Plant Personnel to change the Pollution Control equipment in the existing Power Plants installed during early days. India can ill- afford to replace all the ESPs with the new ones.To renovate the existing pollution control equipment, following methods are being practiced

      • Filling the dummy fields (Casing without internals were installed at the initial stage)
      • Introducing intermittent charging
      • Adding series fields to the existing ESPs
      • Adding Series ESPs in a place available very close to the boiler
      • Placing one more ESP parallel to the existing ESP
      • Replacing the internals and adding new internals by increasing the casing height
      • Introducing New ESPs in the existing space.
      • Introducing bag filter in the existing ESP casings

      The above approaches have been implemented and operating in India for more than 100 installations which include applications like Coal fired boilers, FBC boilers, stoker fired boilers, recovery boilers, cement plants (kiln, clinker cooler, coal mill) etc.

      Each case is unique in nature and to be evolved with due consideration to many in-situ factors

      Since the pollution norms are becoming stringent in many other parts of the world, e.g. South Asian Countries, the above methods of retrofit would be useful to enhance the pollution control equipment.

      This Paper deals with the need for retrofitting, the various options available, the constraints being faced normally, selection criteria for the particular option, the benefits accrued, the response of users with case studies.

  • b07 application of wp type electrostatic precipitator for sinter band.
    • Problems of electrostatic precipitator for sintered tail flue gas are introduced briefly. Technical parameters and structure features of WP type electrostatic precipitator are emphasized. By real operation in Anyang Iron and Steel company, it was proved that WP type electrostatic precipitator worked satisfyingly.
  • b08 conditions for electrostatic precipitators after biomass fired boilers.
    • Efforts are made to increase the use of renewable energy sources to limit the fossil fuel combustion. In 2001 combustible renewable fuels including waste represented slightly more than 10% of the primary fuel supply globally.Solid biofuels are fired in small units for domestic heating, in grate boilers for district heating and industrial utilisation and in fluidised bed boilers with thermal capacities exceeding 100 MW. Biofuels are also used for co-firing in pulverised coal fired boilers.

      There is an increasing concern regarding the particle emissions from biomass combustion. This paper will discuss particle characterisation and particle collection after biomass fired boilers with a thermal capacity exceeding 1 MW. The smallest boilers in this range are often only equipped with a multicyclone for collection of the coarse particles in order to meet rather modest particle emission requirements. Larger boilers have more stringent requirements, which need efficient removal also of the fine particles. The electrostatic precipitator (ESP) is the most common choice, due to its robustness and high particle removal efficiency for the complete particle size range.

      This paper will deal with properties of particles formed in biomass combustion and the influence on the ESP covering different types of biofuels. Comparisons will also be made with coal combustion.

  • b10 design and fea of a linear electrostatic motor.
    • A linear electrostatic motor was proposed and analyzed by using FEA method. The device consists of a single 3-phase electrode structure stator sheet which drives a nonconductive slider directly via electrostatic force. Stages of the operation respectively are (a) electrostatic charges are induced over the slider surface (b) stator polarity changes (c) a motive force is appeared between the stator electrodes and slider and consequently moves the slider. In this paper, we analyzed the magnitude of attraction and repulsive forces caused by applied voltage on stator and conversely, we calculated the least needed voltage to create motive force. This simple structure of device can be used in many fields such material handling, positioning system and separators. Because the electrostatic forces are distributed over entire surface of slider, it can drive both thin and delicate nonconductive material. Since performance is sensitive to humidity changes, this electrostatic technology needs a dry ambient to operate .Some experiments were conducted to verify the functionality of the proposed linear electrostatic motor, during the experiments many nonconductive material such as paper and cloth have been tested as moved material and could be propelled when the relative humidity condition was less than 30%.
c 1-5 series – cold plasma and other technologies (wednesday, may 19, 2004)
  • c01 all – solid state pulser design for a pulsed corona flue gas pollution mitigation system.
    • This paper reports on progress made with the design, construction and experimental evaluation of the pulser equipment on a Flue Gas pollution mitigation system, used for on-line testing and flue gas characterisation by Tswane University of Technology and Eskom Holdings. A separate paper reports on the layout, use and the results achieved with the mobile facility on which this equipment is mounted.
  • c02 latest developments of the plasma-enhanced electrostatic precipitator for mercury removal in coal- fired boiler flue gas.
    • The plasma-enhanced electrostatic precipitator (PEESP) is an innovative coal-fired boiler flue gas mercury removal system that combines existing electrostatic precipitator technology with low-energy plasma technology. This new technology is energy efficient and produces very little secondary waste as compared to baseline absorbent mercury removal technologies. In April 2002, MSE Technology Applications, Inc. (MSE), and Croll-Reynolds Clean Air Technologies (CRCAT) were awarded a joint patent on the PEESP technology based on bench-scale experimental work conducted by MSE in February 2000. The original PEESP bench-scale qualitative experiments performed at MSE during the summer of 2000 indicated high mercury removal efficiencies while treating a simulated coal-fired boiler gas stream containing 250 micrograms per dry standard cubic meter (μg/dscm) of elemental mercury. Steam plus oxygen were used as the reagent gas while applying a constant negative high-voltage source to the electrode in a single-element reactor. Bench-scale testing results were reported at AQ3 last. This paper will provide an update on laboratory scale testing in a multiple electrode tubular wet ESP.
  • c03 from electrostatic precipitation to corona plasma system for exhaust gas cleaning.
    • This paper does not intend to review either electrostatic precipitation or corona plasma processing, but to discuss some critical issues when developing industrial streamer corona plasma systems for exhaust gas cleaning. Based on streamer generation and interaction between power sources and reactors, two energization methods, namely HPPS and DC/AC, were developed. The data available would be sufficient enough for commercial-scale design of a corona plasma system for DeNOx, DeSO2 and dust removal. We foresee that by retrofitting available ESP, a plasma based gas cleaning system to simultaneously remove polluting gases, heavy metals, and particles will be applied in the near future.
  • c04 results of the indigo agglomerator testing at watson power station.
    • The Bipolar Electrostatic Agglomeration process used in the Indigo Agglomerator attaches the fine particles, generally smaller than five microns, to the larger particles, generally larger than ten microns. The electrostatic precipitator does not collect dust in the 0.3 micron to 3 micron range efficiently. By attaching these particles to large particles that are easily collected, the Indigo Agglomerator greatly reduces fine particle emissions from coal fired boilers.

      This paper details the results of testing carried out by the Southern Company on a commercial installation of the Indigo Agglomerator at the Watson Power Station in the USA. The precipitators’ performance and operation were evaluated over a twelve month period by comparing the two identical precipitators installed on Watson Unit 4. The only difference between A and B Precipitators is the installation of an Indigo Agglomerator in the B Precipitator inlet duct. This evaluation shows a major improvement in performance and operating condition on B Precipitator, due to reduced fine particles entering this precipitator. An in-situ Process Metrix optical particle size measurement instrument was used to measure the change in particle size produced by the Indigo Agglomerator. These results confirm that the improved Opacity and mass emissions on B Precipitator are due to lower fine particle emissions caused by a reduction in fine particles at the precipitator inlet as a result of agglomeration in the Indigo Agglomerator.

  • c05 mobile facility for on- line flue gas characterization.
    • Eskom Holdings and Tswane University of Technology (TUT) initiated a research project for the mitigation of coal burning power station flue gas pollutants. It was decided to carry out pulsed corona flue gas characterisation on-line in this project on a side-stream at an operating pulverised fuel burning power station. In this, removal energies against removal percentages would be determined for NOx and SOx to furnish design information for an all-solid state driven pilot De-NOx and De-SOx pulsed corona unit. A mobile laboratory unit was constructed for this purpose and has been used to evaluate the effectiveness of the solid-state pulser equipment and on the flue gas characterisation. This paper reports on the layout of the mobile facility and on the flue gas measurements. A separate paper reports on the design, modelling and operation of the pulser equipment itself.
c 6-8 series – cold plasma and other technologies (thursday, may 20, 2004)
  • c07 light emission from the surface of spike-type discharge electrode at negative corona discharge in a non-thermal plasma reactor.
    • In the past, many experimental investigations for glow or streamer corona induced plasma were conducted by digital real-time or high frame-rate charge-coupled device (CCD) cameras. In this work, the light emissions observed by the CCD camera and optical spectrometers were compared and used in numerical analysis in order to determine the effect of applied voltage as well as the geometry effect in a non thermal spikeplate plasma reactor. Normalized wavelength intensities of the second positive band of nitrogen (wave length 310 to 340 nm and normally proportional to plasma density) show a symmetrical distribution around the maximum value. In contrast, the optical emission profile of the visual spectra (wave length from 400 nm blue to 700 nm red) has bimodal distribution that was also observed by a CCD camera. Therefore, the light emission from the CCD camera is not actually representative of a corona discharge or a plasma channel. Hence, all detailed investigations for any discharge plasma applications should be conducted by optical spectrometers.
  • c08 use of computer model to predict esp enhancement with the installation of an indigo bi-polar agglomerator.
    • The Indigo Bi-Polar Agglomerator is a unique fine particulate control device. Installed ahead of an existing ESP, the Agglomerator charges one half of the particles positively and one half negatively. The charged particles are mixed together, agglomerating the finer particles with the coarser ones. A full-scale demonstration Agglomerator has been installed at Plant Watson in the USA on one-half of the 250 MW Unit #4 coal fired boiler. Testing showed a reduction in mass emissions of 45% and a reduction in stack opacity of up to 70%. A computer model was calibrated, based on the performance of the untreated half of the ESP. The calibrated model was then applied to the Agglomerator treated half. After adjusting the model conditions to the flow rate for the Agglomerator side, the mean particle diameter and standard deviation were modified until the predicted emissions and opacity matched the test results. Additionally, in-situ particle size measurements were made that confirm the increased particle size used in the model to predict the ESP performance with the Agglomerator installed.
d 1-4 series – new esp technologies (wednesday, may 19, 2004)
  • d01 on experiences of the application of high frequency power converters for esp energization.
    • In order to improve Electrostatic Precipitator (ESP) efficiency and system cost a new technology for ESP power supplies, high-frequency power conversion, has been introduced. The first paper on commercial installations was presented about ten years ago (EPRI 1995, Toronto). Products based on this technology have been available on the market since 1993. With the first generation of products the applications were limited to small size ESPs. Through the years the scope has widened and today covers many processes. Still, the available power level limits the use on larger ESP bus sections.

      The estimated number, world wide, of installed ESP power supplies based on high-frequency power conversion is close to 1000. This paper aims to evaluate the experiences, which have been gained through these installations. Aspects such as ESP efficiency, cost and reliability are discussed.

  • d03 study on spraying corona discharge technology with grounding discharge electrodes for purifying flue-gas.
    • This study focused on a new electrostatic precipitation technology of spraying corona discharges with grounding discharge electrodes for purifying flue-gas. DC positive high-voltage was connected to collecting electrodes and water discharge electrodes were grounded. A lasting and effective electrostatic removal of dust with minimized drain water would be achieved by wet or semi-wet spraying corona discharges. The experimental researches on discharge characteristics and cleaning effects of both collecting and discharge electrodes by wet spraying corona discharges were carried out. The treating circulating water and the removing gas contaminant by corona plasma were analyzed. The discharge characteristics of semi-wet corona discharges also were researched. The advantages of spraying corona discharges with grounding discharge electrodes for purifying flue-gas were discussed. The researches have supplied the foundations of theory and design for purifying the flue gases with fine and adhesive dusts using spraying corona discharges.
  • d04 study on magnetic seal technology of ash unloading device with impeller of eps.
    • The seal problems of ash unloading device with impeller under hopper are very common and important to the successful operation of an electrostatic precipitator. Hoppers become plugged and air ingress causes collected ash to re-entrain resulting in increased emissions, and these rigid seals are subjected to excessive wear and need frequent replacement. This paper discusses an advanced powder magnetic seal design that installs permanent magnets at the top of vane and utilizes the magnetism in the Fe3O4 in fly ash to seal the space between the vanes and the walls. The device does not wear and does not need frequent replacement, and the pressure of air seal can be 50kpa.
  • d06 particulate reduction using a series of esps in a coal based thermal power plant
    • Performance of Electrostatic Precipitator (ESP) deteriorates over the years and they are not able to meet the required emission standard. In the present paper we discuss the performance of ESP’s in a power plant, which is situated right in the centre of a mega city. As the power plant is surrounded by densely populated area of the city the other emmision control methods like flu gas treatment with SO3/NH# cannot be applied due to a further risk of pollution. Pulse charging methed has also limited scope of further enhancing the particulate collection efficiency of ESPS. The decision was taken to put additional unit of ESP along with existing unit of ESP. Performance Guarantee (PG) tests were carried out for the whole ESP systems. Samples were collected from the inlet and outlet of the each ESP systems. The collection efficiencies were determined for individual and for the whole set of ESPs. The results indicate a significant deterioration of collection efficiency old ESP unit at the level of (90-93)% against designed value of more than 99%. The new ESP unit, which was put ahead of old ESP unit, was operating in the range of (93-96)% of collection efficiency. The over all Collection efficiency of the system exceeded all the time more than 99.5%.
  • d07 electrostatic sieving precipitator
    • The paper relates to a screen-based electrostatic precipitator suitable for efficient removing of both large and fine particulates from a gas stream. Presented are the results of extensive bench-scale experiments.

      In this apparatus the particulate laden gas is passed through a plurality of closely packed parallel wire meshes in a form of fine plane screens, set perpendicular to the direction of gas flow and connected to a high voltage source. Normally, all screens have the same polarity and all particles as well. This promotes agglomeration of fine particulates inside the screen openings, rather than on wires, and their combining with large particles, which are then captured easier. The precipitator combines conventional sieving and electrostatic precipitation, enhancing the particulate capture through inertial impaction and interception, field charging and diffusion, all in laminar flow conditions.

      Having the same polarity, screens can be closely packed and a high voltage can be applied virtually without limits and without shortcuts. All this results in high collection efficiencies, as well as in drastic reduction of precipitator’s size.

      Also discussed is a slightly modified version, in which the screens can have different polarities, which, in addition to precipitation, could also be suitable for sorting/classification of collected particles, in general, and in flyash beneficiation in power plants, in particular.

      Finally, the precipitator can be modified to operate at as high temperatures as 1500 0F.

  • d08 fractional efficiency of electrostatic precipitators versus skew flow gas technology
    • The skew flows gas technology occurred in the 80`s of last century as a convenient method for electrostatic precipitators (ESP) performance improvement.

      In the professional literature one meets three forms of gas velocity distribution in ESP: uniform flow, linear –skew flow and concave-convex flow.

      Uniform gas flow is characterised by equal value of gas velocity in each cross section along the ESP.

      In the linear – skew gas flow the field velocity is such formed, that in ESP`s inlet crosssection gas velocity decreases to the top, but in the ESP outlet the velocity arrangement is opposite [1,2].

      Another linear – skew gas flow is such formed that in both inlet and outlet ESP cross-sections, the gas velocities increases to the top [3].

      For the concave – convex gas flow it is characteristic that in the inlet of ESP the field of velocities is concave but in the outlet is convex [4].

      In the past studies of skew gas flows the influence of gas flow on overall ESP efficiency was usually analysed [5,6,7]. Individual investigations performed with computer simulation methods analysed the various skew gas flows, the dust reentrainment [8], and the influence of zones number [9] on ESP efficiency.

      The presented paper refers to computer analysis on correlation between skew gas flows and fractional efficiency.

  • d09 the effect of non-uniform dust distribution on esp performance
    • The prediction of the performance of an Electrostatic Precipitator is usually based on the assumption that the dust is distributed uniformly across the inlet. This assumption conforms to the standard requirements of a uniform gas distribution. The effect a non-uniform gas and dust distribution has on the performance of an ESP has been in discussion for a number of years. The development of a reentrainment model to predict the increase in performance resulting from controlled skew gas flows was first presented and published by Mr A Hein in 1990. However, it was also assumed that the dust concentration is uniform within the bulk of the gas. Where the Art Hein approach suggests a bottom skew at the inlet to the first field, other authors advocate a top inlet skew Based on the Hein re-entrainment model the current work investigated the effect of skew dust concentrations on the required gas distribution to achieve the highest performance. The study was extended to predict performances with non-uniform dust distributions for five Eskom Power Stations. In the case of Camden Power Station a Computational Fluid Dynamic (CFD) simulation was conducted to quantify the gas and dust distributions and the performance predictions subsequently conducted were based on the results of this simulation.

      The study has shown that the pre-settling of dust improves the performance of ESPs and that this effect can be enhanced by adopting various inlet and outlet gas skew configurations. The increase in the predicted performance is dependent on the geometry of the inlet ducting and initial gas and dust distribution and the required distributions cannot be generalised. In some cases a top inlet skew is more beneficial than a bottom inlet skew.

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Work still in progress…

ICESP Conference in Kyoto, Japan