ICESP XII – Nuremberg, Germany, 2011
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 XII ICESP Conference under their respective topic. Click on the title to view paper.
Session 3: Numerical Modeling & Simulation:
A 3D hybrid Finite Element – Flux Corrected Transport technique is proposed to predict the electrical and aerodrodynamic characteristics of one-stage electrostatic precipitator consisting of a corona discharge electrode mounted in the middle of the channel between two parallel collecting plates. FLUENT commercial software is used for calculating the turbulent flow distribution assuming k-ε flow model. Two discharge electrode configurations are considered: smooth cylindrical wire and flat tape spiked electrode, where the electrohydrodynamic flow patterns and various particle concentration effect on corona discharge current, airflow velocity and the precipitatipon performance in removal of fine particles are compared.
Some Aspects of “Long Term” Modeling of Electrostatic Precipitators
Nowadays modelling of collection efficiency in electrostatic precipitators is commonly examined by using numerical models. Different models exist for simulation of the multi-variable complex system of ESPs, the several determining physical processes [1]. One group of them determines the particle trajectories inside a half channel of a precipitator assuming that they were more or less the same during the operation of the precipitator. Advanced models take it into consideration, that some phenomena in the ESP build up in a longer time period, so the calculated trajectories must be modified as the function of time, too. One of these basic, typical phenomena is the formation of back corona [2]. Some other phenomena (e.g. changes of environmental parameters and the pollutants stepping into the chamber of electrostatic precipitators) have even longer time constant, so their examination needs much longer period of time. The advanced model described in the paper is able to monitor these “long term” changes explaining some unexpected behaviour of the precipitator. The complexity of the phenomena has been analysed by the newly improved ESP model of the authors, and “long term” simulations have been presented in several case studies of the paper.
Mathematical models of different complexity are developed for the description of the residence time dependent current uptake in a tube wire type electrostatic precipitator under conditions of coronaquenching. For a simple tube-wire geometry, corona quenching by concentrated aerosols is studied theoretically, by numerical simulation and experiments. The numerical simulations are executed in 1D, whereby various levels of complexity (including particle and ion space charge, ion extinction, lateral mixing (turbulent diffusion), particle charge and size distribution, charging and agglomeration kinetics) are attained. Simulation predictions of the current uptake behaviour are compared to experimental results from batch type and continuously operated electrostatic precipitators.
This paper aims at analysis of the monopolar ionized field in electrostatic precipitator (ESP). An iterative finite-element technique is used to solve Poisons equation. We proposed the introduction of a potential corresponding to the critical minimum ionization field directly in the finite element formulation as a Dirichlet condition. The theoretical migration velocity is obtained by balancing the drag force with the Coulomb force or Electrostatic force acting on a particle. We used the model introduced by Cochet for predicting a particle charge. The model assumes that a particle of the same size attains an equivalent maximum amount of charge for a charging time equal to infinity.
Session 4: High Voltage Power Supplies:
In the development of switched mode power supplies (SMPS) different topologies and power devices have been used to provide optimum power supply for electrostatic precipitators (ESP). Different generations of SMPS will be shown below. More than 20 years after the development of the first SMPS for electrostatic precipitation, sufficient experience in improvement of performance has been collected due to many operating ESP applications. With pre-tests and test installations the potential for improved collecting efficiency can be identified before SMPS are permanently installed. Conducted modernizations have shown remarkable ESP performance increase. The typical installations of SMPS at the gas inlet fields tend to provide synergy effects for better performance even in the subsequent fields. However, the degree in increase of achievable collecting efficiency depends on the process conditions. In particular, proper mechanical state of the ESP is essential for optimum performance.
Numerous articles and industry reports have documented the collection improvements obtained by DC mode operation of switchmode HV power supplies when compared with conventional TR-thyristor systems. Several articles have reported that improved intermittent energization (IE) of the ESP field can be obtained using a switchmode HV power supply. The focus of this paper is to examine the operation of switchmode HV power supplies in IE mode. The paper will review electrical operation of IE in conventional TR systems compared to switchmode units, discuss user experience at a site utilizing IE mode and present the electrical performance of the ESP field in IE mode.
4th generation of Coromax pulse generators for ESPs
The first plants using the latest generation of Coromax pulse generators for ESP´s have been commissioned. The present paper will present the new features developed as well a comparison with competing types of power supplies for ESP’s. Among the new features, the use of single IGBT’s as main semiconductor switch and extremely narrow pulses can be mentioned. Furthermore the results obtained after the commissioning of a sinter plant producing 15.000 t/d will be given.
Aspects on high frequency power supplies for ESPs
High-frequency power supplies were originally introduced on the ESP market by ALSTOM (SIR) in 1993 [1, EPRI/DOE 1995]. An evaluation of the experiences gained during the first decade of operation was presented in [2, ICESP IX 2004]. It was found that the dust emissions were significantly reduced at the majority of the installations. Following the introduction of the first products, having a limited power capability, intense R&D efforts have been made in order to make this technology applicable to all sizes of ESPs. At higher power levels the efficiency and the operational temperatures are key design parameters.
It is the objective of this paper to present recent findings on the optimization of design and operation of high-frequency power supplies for electrostatic precipitators. Specifically, operational efficiency and availability will be discussed. Results from lab tests as well as operational data from the installed fleet (>2000 units) will be presented.
Session 5: Fundamentals:
Since January 1st, 2008, the coal power plants are subject to new stricter European Environmental Regulations. To fulfil these new stakes, new and existing units were equipped with denitrification system (such as Selective Catalytic Reduction processes) in addition to the electrostatic precipitators (ESP) and wet-flue gas desulphurization (wet-FGD).
The ESP particle collection process performances mainly depend on:
- The residence time of dust inside the ESP
- The physico-chemical properties of dust (size, chemical composition, resistivity),
- The voltage applied to the dust collector
Only this last point is linked to the ESP itself while the other two depend on other external parameters.
This article focuses on these external parameters and makes the analyses of their impacts on the collection performances.
In particular, we describe and analyse the impact of:
- Coal characteristics through more than 500 reliable coal chemical analyses (from South Africa, Australia, China, Poland, Indonesia, Norway, Poland, Russia, USA coal supplies),
- Residence time, resistivity and collection performances of the 500 coals analysed through software simulation,
- SCR process impacts on the resistivity and the particle size through SO2 oxidation into SO3 as well as the possible production of ammonia sulphate and bi-sulphate species.
Model Calculation of Negative Wire – Cylinder Corona Discharge Properties in Humid Synthesis Gas
For the final clean-up of the synthesis gas produced from a small scale biomass gasification plant having a gas flow rate of 35 kg/hr a wet ESP has been designed and tested. Design was supported by model calculations of the current-voltage characteristics of the wire-tube precipitator. Electronic and ionic properties of multi-component gas mixtures were evaluated from cross section data using a Boltzmann code and ion mobility formulas. Both for synthesis gas and humid air simulated corona inception voltages exceeded measured ones for about 20-30 %, and simulated currents were 20-30 % too low. That measured corona inception voltages are too low can be attributed to the surface roughness of the wire used. Electrons contributing to the current in the drift region of the corona are assumed to be the reason for the larger currents observed in the experiments.
This paper presents a new model to calculate fly ash Resistivity based on its chemical composition, for fly ash generated in Indian thermal power plants, which is one of the critical parameter that influences the fly ash collection, sizing and performance of electrostatic precipitator. The model developed for calculating the electrical Resistivity was verified through, experiments, which were conducted for the measurements of electrical Resistivity over a wide range of temperatures (90 – 455) 0C as per IEEE standards. Around 50 samples were obtained from different power plants in India for the Resistivity measurements, the chemical composition of each sample were determined. These empirical relations provide better agreement with experimental values compared to those developed by Bickelhaupt and those developed earlier in this lab in the working range of operations of Indian ESPS.
The use of electrical corona discharge opens broad possibilities for effective development of electrostatic precipitators (ESPs). The object of the work is the study of the corona discharge in different gases at high temperature / high pressure (HT/HP) conditions. The studies are carried out in a HT/HP ionizer in the pure synthetic air, N2, He and He-synthetic air and He-N2 gas mixtures. Corona discharge characteristics are measured in electrode gaps of 10 mm and 15 mm. In the synthetic air, the corona onset voltage increases with increase of gas pressure. At constant applied voltage, the gas breakdowns take place at a lower pressure while for a higher pressure the corona discharge may not start yet. The stable corona discharge in dense He is observed at gas pressure up to P=10 MPa. For negative corona current is higher than for the positive corona. In the gas mixtures of ca. 50 Vol. % He in synthetic air or N2, the stable corona discharge is observed at higher pressures comparative to pure gases. In helium, corona onset and operation voltages increase linearly with increase of gas pressure. The current-voltage characteristics (CVCs) can be approximated by a polynomial equation rang 2.
Session 6: Precipitator Design:
In this work the influence of gas distribution and field velocity on the electrostatic precipitator (ESP) separation efficiency when using either a conventional T/R-set or a High-Frequency power supply was investigated. The tests where focused on small scale industrial ESP’s for biomass combustion systems in the range of 300 kW to 2 MW thermal power. A small scale industrial ESP which could be equipped with different perforated screen combinations in the inlet section was used to investigate the influence of two different power supply techniques on the separation efficiency when using different gas distribution systems and altering gas velocity within the electrical field of an ESP.
Dust Removal Method of DC Supply Ultra-Wide Electrode Distance
This article is the summary of series paper of “Dust Removal Method of DC Supply Ultra-Wide Electrode Distance—The Theory Overturning for Dust Removal Method of Best Spark Rate”.
This article will formally introduce three important invention achievements (including a number of invention patents and utility model patents):
First achievement: theory overturning for dust removal method of best spark rate. Relate to: control target (fm); form of electric field (structure of narrow electrode distance); form of power supply (frequency power supply).
Second achievement: dust removal method of DC supply ultra-wide electrode distance. Relate to: control target (do), accurate control target (Io); form of electric field (structure of ultra-wide electrode distance); form of power supply (DC supply).
Third achievement: “rectangle method” on automatic following control to dust concentration. Relate to: accurate control target (Io); principle of “rectangle method” on automatic following control to dust concentration; F-series DC high voltage power supply with rectangle characteristics;
Therefore, we can reach a firm conclusion: (1) The dust removal method of best spark rate and its theoretical basis have theory overturning; (2) The dust removal method of DC supply ultra-wide electrode distance and its theoretical basis have been established, which will replace the historical role of dust removal method of best spark rate; (3) The DC power supply with rectangle characteristics is the preferred power supply, which will replace the historical role of frequency power supply.
Recent Technology of Moving Electrode Electrostatic Precipitator
In China and India which are achieving strong economic growth, air pollution caused by emissions from coal-fired power plants and steel plants is a serious problem and therefore these countries are rapidly tightening their emission standards. Since these emerging countries have abundant coal resources, coal is expected to account for a majority of their energy resources and it is therefore imperative for them to install flue-gas treatment equipment for their existing coal-fired power plants and steel plants as well as new ones. Our Moving Electrode Electrostatic Precipitator (MEEP) with its unique technology offers superior collection of highly resistive dust such as coal ash and sintered ash and we will enter the market with this core technology. This technical report describes our development of the new MEEP, which substantially reduces the dust-collection area and facilitates maintenance, to reduce cost and maintenance work.
Session 7: Industrial Applications:
This article presents the results obtained with the dedusting system of the primary mixer’s stack, existing in ArcelorMittal Monlevade’s Sintering Plant – João Monlevade Plant, in Brazil. The dust is collected by means of a recently installed ElectroStatic Precipitator (ESP). The primary mixer’s wet gas is heated with gases from the sinter cooler and, then, introduced in the precipitator inlet duct. The innovation here is the use of hot gases from the cooler to achieve this objective and to adapt the mixture for collection in the ESP.
Starting from ArcelorMittal Monlevade’s need – the primary mixer’s stack dedusting – it was proposed the unique possible solution, but without previous references in Brazil. In most Steel plants, the sinter cooler heat is simply lost in the atmosphere.
Besides reaching the main objective (outlet dust emission < 50 mg/Nm3-dry), the relevant facts of using the sinter cooler heat and improvement of precipitability conditions of the gaseous flow containing dust made this project to be a technical success of performance. It can contribute a lot to new applications.
The initial fear of the high moisture of the mixer’s gases and the particulate matter generated in the mixture of water, lime and the primary mixer’s dust did not come true and the project’s results demonstrated that it was highly reliable, without risks and with good process and constructive performance. For such, studies and calculations were made necessary, allied to the dedusting systems experience of ENFIL.
The Research on ESP Adaptability For Chinese Coal Under 30mg/m3 Dust Emission
Electric precipitator plays an absolutely leading role in countries such as Europe, America, Japan, etc. which have issued much more strict dust emission regulation. But the emission standard of 30mg/m3 to be stipulated by China makes china’s some management departments and users express concern about the ESP. 122 types of China domestic coal which are used in Chinese power plants in recent 3 years are analyzed, furthermore, the performance of ESP which are in operation is studied. The textual criticism on ESP adaptability for China domestic coal is fulfilled. The result shows that ESP can meet the dust emission demand of 30mg/m3 with good economy for 86.06% of the China domestic coal. Thus, ESP still has continuing broad adaptability and is the most ideal dust removal equipment which is wholly suited to conditions in China.
The Gas Suspension Absorber At Norcems Brevik Plant
In the cement industry many plants are looking for ways to reduce their gaseous emissions to comply with new environmental laws. Such is the case with the Norcem plant in Brevik, Norway, which committed to reduce emissions of sulfur dioxide (SO2) by 400 tons per year. This is part of the Gothenburg Protocol, an objective to reduce overall industrial sulfur emissions in Norway by 5,000 tons by the end of the year 2010. To accomplish this, a semi-dry scrubber system called a Gas Suspension Absorber (GSA) was purchased in 2009 and installed in early 2010 as an alternative to a more costly wet scrubber. The GSA system has been commissioned and optimized during 2010 and initial test results indicate that the Brevik plant will achieve their new emissions targets for SO2, as well as reducing emissions of hydrochloric acid (HCl) and hydrofluoric acid (HF). The plant is also well positioned to reduce mercury emissions in the future with the addition of shuttling or wasting dust from the dust collector after the GSA. This paper will review the details of this project and the results that were attained.
Due to recent higher quality requirement for oil-refined-products, sulfur content is increasing in the residual materials, which are used as boiler fuel, from economical reasons and viewpoint of effective resource utilization. In such case, reducing SO3 such as high as 120ppm in flue gas is needed to avoid corrosion and bluish plume. Herein, experiences of improving energization difficulties and clogging in hopper in ordinary “Ammonia Injection + Dry-type ESP” system, according to the intermediate byproducts of NH4 – SO4, are introduced. Furthermore, “Salt Solution Spray + Wet-type ESP” system, which enables more stable and continuous operation, is also introduced.
Session 9: High Voltage Power Supplies:
Study of DBD electrostatic precipitator under pulse and square energizations
This experimental work is aimed at evaluating the effects of the high voltage waveforms (sine, square and stair) on the efficiency of a wire-to-square tube electrostatic precipitator using dielectric barrier discharge. The input parameters under study are: the high voltage magnitude, its frequency and the tube section. The collection efficiency of the electrostatic precipitator is calculated by measuring the concentration of incense particles (average diameter of 0.3 µm) at the outlet using an aerosol spectrometer.
Mobile HV Test System with IGBT Inverter Technology for Electrostatic Precipitators
The system performance of ESPs is considerably influenced by the type and capability of the highvoltage power supply. Switched mode type power supplies – like IGBT inverters – have proven very beneficial for this purpose during the last decade in many applications. Unfortunately, it is very difficult to define exactly the improvement in ESP efficiency prior to the installation of the IGBT based power supply. There are many different process variables and uncertainty factors which cause the theoretical results to be unreliable. Therefore, a practical and reliable determination of possible improvements requires a trial installation of the entire high-voltage power supply equipment on site and accurate analysis of the measured data. The proposed solution features a mobile self-contained trial unit, which can be connected easily to any electrostatic precipitator to run the tests in a real environment. A significant increase in electrical power could be shown in many applications – e.g. a factor 2 could be achieved – which lead to significant improvements in the dust collection performance. Additionally, the energy efficiency of the precipitation process has become more important. With the switched mode power supply technology both collection and energy efficiency can be improved. With the mobile HV test system and the IGBT inverter technology, test results show exactly the possible extent of improvements in ESP efficiency under real-life ESP and plant operating conditions.
An ESP using bipolar-discharge with DC high voltage for road tunnels
Two-stage-type ESPs (electrostatic precipitators) are composed of ionizers and collectors. DC high voltage is applied to the discharge poles in the front stage ionizers. Particles passing through the space of positive or negative corona are charged. The rear stage collectors capture the particles. Although spike-typed dischargers are adopted widely, the spikes in this test are arranged not only in the voltage-applied plates but also in the earth-plates in the ionizer. As the test result, particles are collected by the discharge from both the voltage-applied plates and the earth-plates. The discharge in earth-plates generates ions with opposite polarity to that of voltage-applied plates. This bipolar collection method with the simultaneous positive-and-negative discharge shows a possibility that particles are efficiently captured not only on earth-plates but also on voltage-applied plates in the collector. This study implies the bipolar-discharge ESPs are suitable for smaller ESPs.
Session 10: Biomass:
Biomass co-firing. New challenges in electrostatic precipitators
Power plants are the most important sources of atmospheric contaminants. It refers equally to conventional, coal-fired, as well as biomass co-firing plants. Biomass burning causes new operational problems in electrostatic precipitators. Although there are an increasing number of publications on troubles encountered in biomass co-firing boilers, there is still low number of papers on experimental or operational results regarding the electrostatic precipitators cleaning the flue gases from co-fired biomass. These new problems arising in electrostatic precipitators result from the fact that these precipitators were designed for burning the coal, which is of different chemical composition than the biomass and the physical properties of fly ash are also different. The differences in flue gas composition, particularly variations in particle size distribution in submicron size range, increased emission of CO, and tar leaving the boiler. These new after-burning products, can cause degradation of construction elements of ESP, for example, chlorine or sulfur corrosion of metals, degradation and contamination of HV insulators, etc. Tar present in flue gas after wood burning can, after a longer time, be deposited onto the insulators, changing their electrical properties and causing an increase in leakage current or even the surface breakdown. It was reported in the literature that increased amount of CO in the flue gases can result in fires in ESP. It seems plausible that the same problems will be encountered in ESP cleaning flue gases from biomass burning boilers. The long-term effects of cofiring on the electrostatic precipitator are, however, not known.
There are also met some reports on positive aspects of biomass co-firing for ESP operation. It was noticed that the emission of SO2 and NOx is reduced when a small amount of biomass is added to the bituminous coal, due to Ca, K and Na content in the biomass. The emission of SO3 is also decreased because of high concentration of CaO in the fly ash. However, due to the reduction of SO3 and low content of unburned coal in fly ash, the flue gas conditioning would be necessary in order to prevent the back discharge in ESP. This effect can be slightly compensated by higher moisture content in flue gas after biomass co-firing.
The purpose of this paper is to outline some new aspects of the effect of biomass co-firing on the short- and long-term operational properties of electrostatic precipitator. The considerations are based on preliminary reports met in the literature and some experimental results of the authors
Development and study of an electrostatic precipitator for small scale wood combustion
Wood is often combusted in small scale units for domestic heating. Although the total particle emission levels in Germany have declined steadily over the years, small scale wood combustion is an increasing source of indoor and outdoor air pollution. A novel space charge electrostatic precipitator (ESP) was developed for control of fine particle emissions control from wood combustion stoves and boilers. The ESP ionizer consists of a high voltage isolator, a screen electrode and star-form corona discharge electrode. The charged particles are precipitated in the collector which includes a grounded brush. In the article the results concerning the influence of combustion conditions in the wood-log stoves, gas temperature and flow rate, particle number and mass concentration and values of applied voltage and corona current on the ESP collection efficiency are discussed. For steady flame combustion, the mean mass collection efficiency of the ESP is ηM=87±3% for 13% O2. The fractional collection efficiency of the electrostatic precipitator is ηN>90%.
Charging and removal efficiency of an ESP in a 250 kW biomass boiler
The combustion of biomass creates ultra fine particulate matter which is not precipitated by traditional multi cyclone technique, usually adopted on small scale plants. In Sweden the number of small bio fuelled plants is increasing and there is a need for cost effective means to precipitate the ultra fine particles formed. One such technique may be electrostatic precipitation, but the economy of scale is a constraining factor for systems commercially available today. This paper describes field tests of a low cost electrostatic precipitator, ESP, including not only investigation of collection efficiency, but also measurement of charging effectiveness. The aim of the tests was to determine the potential for the low cost ESP design to form part of an electrostatic precipitation system for use on bio fuelled plants in the megawatt scale. The charges acquired by the particles have been measured using a low pressure cascade impactor, ELPI. Measurements of charges were carried out on particles escaping from the ESP. The results of the measurements of particle charges indicates that the method may correctly reflect the mean charge levels of particles of the different sizes usually found within the fine particle mode of flue gases from biomass combustion.
Session 11: Pulsed Power:
Laser diagnostics of pulsed corona discharge
Laser diagnostics of atmospheric-pressure pulsed corona discharge are introduced. Density of radicals (OH, N, O, O3, N2(A)), vibrational temperature of N2 and O2, and translational temperature are measured in the pulsed corona discharge using laser-induced fluorescence (LIF), laser absorption, and coherent anti-Stokes Raman scattering (CARS). Their spatial profile and temporal evolution after the pulsed corona discharge are measured to study the chemical process in the postdischarge period.
This paper is aimed at investigating the nitrogen oxides (NOx) removal using dielectric barrier discharges (DBD) in a wire-cylinder reactor filled with dielectric pellets and stressed by high pulse voltage. The effects of various parameters (the voltage amplitude, frequency, gas flow rate, and use of dielectric pellets) on the discharge power, NO removal efficiency and NOx concentration have been studied experimentally. Two dielectric materials (ɣ-alumina and glass pellets) were evaluated for their ability to reduce NOx using non-thermal plasma. To reduce the NOx concentration, the output of the plasma reactor was pumped into sodium sulfite (Na2 SO3) solution with different concentrations to absorb NO2. It has been found that the discharge power and NO removal efficiency increase with the increase of the applied peak voltage and frequency. On the other hand, the discharge power is independent of the gas flow rate, while the NO removal efficiency increases with the decrease of the gas flow rate. The NOx concentration decreases with the increase of the applied peak voltage, frequency and concentration of Na2 SO3 solution, while the NOx concentration decreases with the decrease of the gas flow rate.
Deodorization System Development by using Positive Pulsed Corona Discharge
Pilot deodorization system experiment by using plate-rod positive pulsed corona discharge had been performed to evaluate removal efficiency for waste food dry recycling plant flue gas and to attest scale-up ability. As result of analysis of flue gas material composition at inlet and outlet, about over 50% odor materials are converted to non-odor molecular at electrical potential difference of about over DC 30kV and DC with pulse 42kV on positive pulsed corona discharge
Pulse-mode operation of high-frequency power supplies for ESPs
High-frequency power supplies were originally introduced on the ESP market in 1993 (ALSTOM/SIR). Initially the high frequency power supplies were most often installed on low- to medium-resistivity applications due to limited power capabilities. During the last years more powerful models have been introduced, which are suitable for utility installations. In many cases these are burning coals, which produces a high resistivity flyash.
When applying high-frequency power supplies (HFPS) to high-resistivity dust applications, pulsed mode operation needs to be applied in order to avoid back corona. It is the objective of this paper to present pulsed mode operation of HFPS. Different aspects, such as: pulse parameters, spark-overs, and the resulting ESP-voltage and -current waveforms will be discussed. Results from power-plant (coal) installations are presented.
Session 12: Back Corona:
ESP Controls For Various Fuel Boilers Based On The Odeus Method
The article presents the principle of ESP control for a boiler burning with different fuels. To develop the principles of ESP algorithm the ODEUS method for object creating and managing was a better solution.
With the ODEUS method a designer or a manager of ESP control system makes sure that all aspects of complex design, management or control will be exhausted and implemented efficiently. The key features of this method are the binary system (for each problem there are two contradictory potential solutions) and the pyramid principle (all systems consist of elements, all processes consist of operations).
Back Corona and Resistivity Measurements: New Findings
Electrical resistivity of the dust, to be separated in an electrostatic precipitator, is an important parameter from the design and operation point of view. It gives the knowledge about the onset of the back corona in the system. In-situ measurements can be performed using a resistivity measurement probe. But mostly it is done in the laboratories using a measurement apparatus and the dust sample collected from the hopper beneath the precipitator. A laboratory setup will be introduced to measure the dust resistivity using a new method. Here, the onset of back corona can be detected directly during the experiment which can be eliminated immediately from the system by reducing the current by controlling the supplied voltage. Experiments were performed with a fly ash sample with 11µm and four glass samples with 75, 112, 278 and 394 µm mean particle sizes. Results will be presented and discussed about the influence on resistivity results of dust resistivity measurement method: point-plate and plate-plate, mode of temperature variation: ascending and descending, air temperature, particle size and air humidity. Finally, the visualization of back corona in such systems will be presented.
Session 13: New Applications:
The history of electrostatic precipitator (ESP) is already longer than a century. Therefore ESP as an investment product is typically regarded as a mature technology with very limited prospects for major development steps. The Ion Blast precipitator technology however means a substantial change to the ESP philosophy and challenges the conventional ESPs. Ion Blast precipitators (IBP) utilize the ionic wind, which is specially indorsed by utilizing a doubled voltage level, up to 150 kV. At the same time the distances have been increased. An Ion Blast precipitator is typically a vertical cellular one-fieldESP with a self-supporting honeycomb structure. The hexagonal cells are significantly larger than in any conventional ESPs, the wrench opening of the cell is ca. 1.3 m. Ion Blast precipitators are highly competitive in price, maintenance costs and efficiency even with the challenging process conditions and in sub-micron particle removal.
Performance of High Velocity Electrostatic Precipitator for Road Tunnel
The particles emitted from diesel engine exhaust have low resistivity and extremely small in the range of 70-120nm. An electrostatic precipitator (ESP) has been extensively used for the collection of these particles. A two-stage ESP using charging section and collection section has been installed for the collection of diesel particles and improving the visibility index in road tunnels. The characteristics of ESP in road tunnels are demanded to process in high gas flow velocity, miniaturization and high collection efficiency. In this study, the underlying data of ESP performance was extracted in condition of high gas flow velocity. The gas flow velocity was in the range of 10 to 25 m/s. The collection efficiency for experiment and the simulation were compared.
Operation of an electrostatic precipitator at a 30 MWth oxyfuel plant.
The performance of a full-scale ESP was studied at the Vattenfall AB oxyfuel pilot plant in Schwarze Pumpe. The lignite-fired boiler has a 30 MWth top-mounted pulverized coal burner and was operated under conventional air combustion as well as oxyfuel combustion. The ESP was operated with varying numbers of fields in service and at different current/voltage settings. Particle number size distributions downstream the ESP were established on-line in the size range 0.015-10 µm, using an electrical mobility spectrometer and an aerodynamic particle sizer. The particle size distribution at oxyfuel operation was qualitatively very similar to the results obtained for air-firing. Gravimetric measurements of total fly ash concentration showed outlet emissions below 5 mg/Nm3 when the ESP was operated with two fields in service at oxyfuel conditions.
Challenges for old ESP Upgrades at Utility with high Resistive Coal/Ash
Coal Fired Utility Stations are one of the major users of Electrostatic Precipitators (ESPs) for particulate emission control. These are primarily Pulverised Fuel Fired Boilers with varying Resistivity & Fineness. The paper generally speaks about the challenges that we face with the old Precipitators to cope with stringent emission norms in spite of Physical dimensional and plant layout Restrictions.
The Resistivity & Fineness are two major criteria for Precipitator sizing for Fly Ash. In such conditions, ESPs really face challenges for a lower emission requirement in front of Fabric Filters in spite of quite a few Operation and Maintenance advantages. Today’s technology has advanced very fast, particularly in the area of High Frequency Power Supplies in combination with Automatic Semipulse Controls really shows extremely promising results beginning usually at 20 % emission reduction, but commonly much better than this – in spite of all the constraints.
Present scenario for such Utility plants may sometimes not even allow a proper shut-down period to replace/rectify defective Mechanical components or to realign critical ESP internals or to carry out a reasonable Gas Distribution and sneakage Tests. For obvious reason, thrust is more and more towards HV, Electronics and Controls to overcome problems in other areas as a substantial portion of the work can be carried out without a shutdown.
In this paper we discuss and compare the emission performance of an Utility ESP plants in Australia.
Session 14: Numerical Modeling & Simulation:
Enhanced Electrical Model for Electrostatic Precipitators
Electrostatic precipitators are used to separate dust loads from the exhaust gases by using electrostatic fields. The electrostatic precipitator has the advantage, compared with the fabric filter, that there does not exist any systematic lower limitation for the dust particle size [1]. For efficient usage of the electrostatic precipitator it is necessary to understand the rather complex electrical model for the precipitators. This model is based on the electrical characteristics of the dust particles and the precipitator construction and exceeds the filter modeling which is described in the electrostatic precipitator’s standards. Besides the resistance values of the dust it also considers the permittivity of the particles and molecules and adds a capacitor. Further on the flashover event is included in the model. Thus the model considers also the dynamic behavior of the precipitator besides the static resistances.
Fig. 3-1: Enhanced Electrical Model for the Electrostatic Precipitator
Power Electronic Modeling and Emulation of an Electrostatic Precipitator
In this paper a power electronic emulation of an electrostatic precipitator is presented. Precipitator power supplies can be tested under real power and operating conditions up to 200 kVA. Energy consumption of the system is very low, because the energy which is drawn by the emulation converter is fed back into the power grid. Therefore, just the power losses have to be provided by the grid. It is possible to implement different precipitator models to verify real plant operation conditions or to optimize parameters for new precipitator designs. Precipitator power supplies can be tested as well in static as in dynamic operation points to verify the proper function of the device in the laboratory.
Modern High-Voltage Control of an Electrostatic Precipitator
A modern high-voltage control of an electrostatic precipitator provides both high separation efficiency and low demand of electrical power. The paper explains the physical background how this pretended contradiction can be dissolved. Motivation for this contribution is the convincing result of an electrical ESP retrofit behind the bituminous coal fired boiler in Maasvlakte / Netherlands.
Session 15: Wet ESPs:
A Conductive Composite Material for Wet ESP Applications
This paper discusses the development of a new carbon composite conductive material for use in wet electrostatic precipitators (WESPs). The objective was to develop a low cost alternative exhibiting improved properties compared to stainless steels and lead. After laboratory evaluation, field trials were undertaken using commercial-grade WESP tubes at two industrial sites. The material was further improved to increase arc resistance, while maintaining corrosion resistance and conductive properties. This new material, found to have better arc resistance than SS304L stainless steel, was used to manufacture a tube bundle and installed in a pilot WESP system.
Modeling the precipitation process in ESPs requires a strongly coupled system of the Maxwellequations, describing the electrical conditions, and the Navier-Stokes-equations to determine the fluid flow. Another task is the implementation of the particle dynamics, i.e. the charging kinetic and the transformation of the Electric field distribution due to the resulting space charge. The purpose of the presented work is the development of a CFD-based designing tool to predict the ESPs precipitation efficiency as a function of important parameters, such as the geometric patterns, electric potential, particle size distribution and concentration.
Fine particle removal of two-stage ESP using water film collection plates and nonmetallic charger
A novel two-stage wet ESP has been developed using a non-metallic carbon brush precharger and collection plates with a thin water film. The electrical and particle collection performance was evaluated using submicron particles by varying the voltages to the precharger and the collection plates. The experimental results show that the wet ESP using 7 L/min/m2 of water that uses carbon brush precharger charged particles with approximately 10% particle loss, while producing concentration of ozone less than 30 ppb, which is significantly lower than the current limits of the international agencies, and achieved a high collection performance of average 90% for ultrafine particles, based on the number concentration at 3-5 m/s through the precharger and 1 m/s through the collection plates.
Wet precips for CCS, Increasing business opportunities for large scale wet precips
Session 16: Monitoring:
New emission sampling system for particle number concentration up to 109/ccm
The GRIMM emission sampling system in combination with a scanning mobility particle sizer allows continuous online measurements of particles in the size range 3nm to 155nm with a resolution of 44 size channels. Single channel measurements can be performed with a time resolution of up to 8 Hz. The system is portable, easy to install, robust, and only needs a power outlet for operation. It is therefore ideal for process control and emission measurements. The precise particle sizing allows a conversion of the measured number distribution in dust mass concentration, online with a software package. The system was tested on several applications, e.g. wood combustion, automotive emissions, emissions of printer and copy machines. Results of number and mass distribution and total particle number and mass concentration will be shown with respect to different emission sources and operation settings. Due to the easy operation and fast response the system is suitable for online testing of emission sources, both and mitigation techniques like filters or precipitators.
Direct measurement of ESP charging efficiency with Electrical Low Pressure Impactor +
Electrostatic precipitator particle removal efficiency is governed by the level of charge that the particles gain in the ESP. The ELPI+™ measures real-time (10 Hz) particle size distribution and concentration in the size range from 6nm to 10 µm. As a unique feature of the instrument ELPI+™ can also measure the size resolved number of charges per particle. In this work we will present ESP charging efficiency measurement data along with discussion on factors that affect the performance of ESPs.
Session 17: Diesel Exhaust Gas Cleaning:
Novel EHD-Assisted ESP for Collection of Low Resistive Diesel Particulates
The novel electrohydrodynamically-assisted electrostatic precipitator (EHD ESP) was developed to suppress particle reentrainment for collection of low resistive diesel particulates. The collection efficiency was compared between the EHD ESP and the conventional ESP using two large diesel engines; 2.3 L and 3.2 L engines. The gas velocity was varied in the range of 1.35 to 7.3 m/s and the load was set at 0, 25 and 50%, where the operating gas temperatures were varied from 120 oC to 280oC for 3.2 L engine. The particle size dependent collection efficiency was evaluated for the particle size ranging in 20 to 5,000 nm using a scanning mobility particle sizer (SMPS) and a particle counter (PC). The EHD ESP showed excellent suppression of particle reentrainment and collection efficiency even for high gas flow velocities in comparison with the conventional ESP.
Diesel PM collection for marine emissions using double cylinder type electrostatic precipitator
Collection of low resistive particulate matter (PM) generated from marine engines or diesel generators have been known to be difficult by the conventional electrostatic precipitators (ESP). In this study, the double cylinder type ESP was developed to remove the low resistive diesel exhaust particles. Two(W=C ESPs, namely, the conventional single cylinder type ESP (S-Cylinder ESP) and W-Cylinder ESP were investigated using a 6728-cc engine. The particle size-dependent collection efficiency was obtained using a Scanning Mobility Particle Sizer with particle size in the range of 40 – 500 nm and a aerosol spectrometer with particle size in the range of 300-17,000 nm. The particle mass collection efficiency was obtained using a Low Volume Air Sampler. The effectiveness of re-entrainment or collection efficiency for two ESPs was compared. As a result, the conventional S-Cylinder ESP showed good collection efficiency for particle sizes less than 300 nm but showed severe reentrainment for particle size greater than 1000 nm. W-Cylinder ESP also showed good collection efficiency for particle size less than 300 nm. However, the collection efficiency for particle size greater than 1000 nm was significantly improved due to suppression of particle re-entrainment. This result was also supported by the particle mass measurement and the filter color determined by the LVS. (Spell out).
Diesel exhaust particle reduction using electrostatic precipitator
Electrostatic precipitators (ESPs) are used to decontaminate polluted environment. Conventional ESPs has high collection efficiency but still has a problem in that collection efficiency decreases due to particle re-entrainment for collection of low resistive deisel particulates such as marine engines. In this study, the effect of electrode configuration on collection performance of deisel particulates was investigated using a one-stage and a two-stage ESP. The particle concentration for the particle size ranging in 20 to 5,000 nm was measured using a scanning mobility particle sizer (SMPS) and a particle counter (PC). The collected particles on electrodes were observed usign a scanning electron microscope (SEM). The collection efficiencies as a function of the electrode length and the particle diameter were estimated. As results, the particle re-entrainment was suppressed with increasingn the number of discharge electrode in the one-stage type ESP and increasing the collection electrode length of the collection section in two-stage type ESP.
Electrostatic precipitation of diesel soot
Diesel particulate filter (DPF) has been established as a key technology in reducing diesel particulate emission. However, technological improvements to pressure drop, durability, and insufficient collection efficiency for nano-particles are still required. Electrostatic precipitator (ESP) is another leading technology used in exhaust treatment but it is currently limited to applications for stationary sources. In this paper we have proven that simultaneous use of ESP and DPF show synergetic effects of very high collection efficiency and slower increase of the pressure drop. The number concentration of particles observed downstream of the combined system was 98% smaller compared with that of DPF only. At the same time, it was confirmed that increase in the pressure drop across the DPF was slower about 10% compared with that of DPF only. In addition, regeneration of DPF was also investigated using non-thermal plasma (NTP). In order to generate the plasma inside the DPF, a surface discharge was used in front and a DC electric field was applied across the DPF. In this study, the discharge plasma was used to oxidize PM accumulated inside the DPF. It showed around ten grams per kilowatt-hour (g/kWh) of the PM oxidation efficiency.
Session 18: Biomass & Nonthermal Plasmas:
Comparison of different power supply techniques for biomass ESP applications
This work gives a power supply manufacturer independent comparison of conventional T/R-sets and High-Frequency (HF-) power supplies for biomass electrostatic precipitator (ESP) applications. A comparison of the two power supply techniques and also an assessment of HF- power supplies of two different manufacturers were done at a lab setup. In a second investigation, a HF- power supply was setup beside a T/R-set on an ESP at a 30 MW biomass power plant to investigate the separation efficiency of both technologies under real conditions. Total separation efficiency, as well as fractional separation efficiency, spark response regulations and power consumption were measured.
A plant of low emission hot water or steam supplying system which consists of a multi-fuel boiler (gas or oil fuel) and a plasma-chemical hybrid NOx aftertreatment is demonstrated. The plant can provide renewable energy or carbon neutrality because it can use waste oil or bio-oil. The boiler has a steam generation rate of 2.5 t/h, and the flue gas flow rate is from 650 to 2150 Nm3/h. In city gas combustion, untreated NOx at boiler outlet of approximately 26 ppm is reduced to less than 1 ppm at the outlet of the removal apparatus during a 450 min operation. Bio-oils can be burned without problem and NOx emission of less than 20 ppm is continuously achieved from 110-120 ppm at boiler outlet. The CO2 reduction when heavy oil is replaced with bio-oil, is estimated. Furthermore, the system continuous operation is successfully conducted in accordance with the designated operation conditions for industrial application.
Non-Thermal Plasma Decomposition of Dilute Trichloroethylene in Air Catalyst Effect
High pressure non-thermal plasma decomposition performance for low density, typically 250 ppm, volatile organic compounds (VOCs), mostly trichloroethylene, in synthesized air was examined for various conditions. In order to improve the VOCs decomposition energy efficiency of the plasma reactor, new manganese-dioxide supported alumina spheres were examined, where that catalyst works well to decompose the plasma-produced ozone even at the room temperature. At that ozone decomposition process in the catalyst, the trichloroethylene (TCE) was also oxidized very well. Although the specific energy density (SED: input discharge energy, Joule per 1 litter gas) was rather small, the TCE decomposition efficiency was more than 99 % at some conditions. Still now, the optimal amount of the catalyst was not yet determined. Increasing effect of the catalyst amount was examined concerned with the byproduct behaviour.
Session 19: Fabric Filters:
Fabric Filter Optimization using Computational Fluid Dynamics
Optimal filter performance requires proper gasflow and dust distribution on the filtration area. Fabric Filters are especially sensitive to uneven flow, as premature bag wear immediately increases particle emissions. In addition, upgrading existing installations has become more challenging due to strict emissions regulations and common physical and dimensional restrictions on existing equipment, so proper flow distribution becomes critical in maximizing overall fabric filter performance. Computational Fluid Dynamics (CFD) modelling of the gas flow is becoming a valuable tool in designing, testing and comparing different solutions. In the present study, focus is placed on CFD modelling of different Fabric Filter designs, resulting in custom gas distribution modifications for each. The study demonstrates that CFD is a flexible and a cost effective alternative method to the traditional approach of model or full-scale tests on new Fabric Filters, Electrostatic Precipitators to Fabric Filter conversions and in Air Pollution Control (APC) equipment in general.
High Performance Filtration In Situ Testing of Filter Media in Coal Fired Boiler Bag Houses
Filter materials and filter bags are designed to suit the process environment and the particulate emission limits required by the air pollution regulatory bodies. Composite materials combining different fibres are used to achieve a filter media with superior characteristics and more cost effective. The presentation gives an overview on the properties of high efficiency filter media and fibres designed for coal fired boiler bag houses including the filtration mechanism associated with high efficiency filtration. Testing of a new filter media is of crucial importance before the large scale implementation in a bag filter unit. The paper describes a new concept and equipment for in-situ testing of bags, filtration materials and fibres, the Evonik Filtration Test Rig (EFTR). With this method, the test bags / materials are exposed to the same process conditions as the filter elements from the main bag house, and the performance of each test bag is monitored individually. Results of various tests are presented and discussed. The EFTR testing is part of a joint research project between Evonik Fibres and Eskom.
Surface potential decay measurements of corona-charged non-woven fabrics for air filtration
The aim of this paper is to discuss the possibility of using the surface potential decay (SPD) curves for predicting the particle collection efficiency of corona-charged non-woven air filtering materials. The slower the SPD, the longer the charge is retained by these materials and the better the particles are captured by the air filter which mainly consists of non-woven fabrics made of thermally pressed polymeric fibers. The experiments were performed on two types of non-woven polypropylene (PP) samples, which are typically employed in the construction of air filters for the air conditioning industry. The fabrics where corona charged using the triode arrangement, which consists of a wire-to-plane electrode system, a metallic grid and a grounded aluminum plate which is in contact with the samples. After charging the samples with negative electric charges, the variation of the electric charges, on the the surface of the samples, was evaluated using the SPD technique. Thermally pre-conditioning the materials may enhance the external charge injection, while maintaining a low relative humidity of the ambient air may reduce the superficial moisture and favor the retention of the charge. The deposition of Teflon nano-particles on the surface of the fibers improved the SPD characteristics of the materials.
Application of Electrostatic-fabric Integrated Collector for 660MW Power unit of Coalfired Boilers
Since 2005, the Electrostatic-Fabric Integrated Collector (EFIC) of LongKing has been applied to coal-fired boilers for dust removal. Until now, we have signed contracts to supply 178 EFIC sets, 91 of these have been put into operation successfully for generating units with capacity from 15-660MW. Currently EFIC application for 1000MW power unit is being manufactured and it will be installed shortly. This paper mainly introduces the application of EFIC for 660MW power unit of coal-fired boilers. Since put into operation in Apr. 2009, it has been running steadily, with a stable dust emission below 30mg/Nm3, and the pressure drop is maintained 900-1000Pa. This is the first time EEIC technology has been applied to 660MW power units. The success of this project is a milestone of LongKing’s EFIC development and application to large scale coal-fired boilers.
Session 20: Mercury Separation:
The behavior of mercury sorbents within electrostatic precipitators is not well-understood, despite a decade or more of full-scale testing. Particulate filters have shown evidence that powdered activated carbon (PAC) can penetrate ESPs significantly during sorbent injection for mercury emissions control. Recent laboratory results suggest PAC collection behaviour in ESPs that is different than fly ash. The present analysis considers a range of assumed differential ESP collection efficiencies for PAC as compared to fly ash. Estimated emission rates of PAC are compared to estimated emission rates of black carbon on fly ash, each corresponding to its respective collection efficiency. To the extent that any emitted PAC exhibits size and optical characteristics similar to black carbon, such emissions could increase black carbon emissions from coal-based stationary power generation. The results reveal that even for the low injection rates associated with chemically impregnated carbons, black carbon emissions can easily double if the fine fraction of the native fly ash has a low LOI. Increasing sorbent injection rates, larger collection efficiency differentials as compared to fly ash, and decreasing sorbent particle size all lead 2 Introduction to increases in the estimated black carbon emissions.
Session 21: Numerical Modeling & Simulation:
Comparison of numerical and experimental results for an electrostatic precipitator
Some fundamental aspects of the electrostatic precipitator are investigated via a combination of tests in a high-voltage rig and numerical computations. The electric field and charge distribution in the duct are computed numerically using the commercially available FEM solver Comsol Multiphysics. The derived properties are compared with experimental data and general operating experience. Overall the agreement between numerical results and experiments is very satisfactory. This provides insight in some basic phenomena governing the precipitator behaviour, and may give qualitative guidance also in the practical design of precipitators.
Experimental validation of numerical models of collecting Electrodes
The paper presents an experimental validation of two models of the collecting electrodes of an electrostatic precipitator (ESP). The first model combines the finite element method used for calculations of spring deformations with the rigid finite element method used to reflect mass and geometrical features [11]. It is called the hybrid finite element method (model: HFEM). As a result, the model with a diagonal mass matrix is obtained. Due to a specific geometry of the electrodes, which are long plates of complicated shapes, the second model uses the strip method (model: SPL). The strip method is a semi-analytical method [2], which allows us to formulate the equations of motion with a considerably smaller number of generalized coordinates. Frequencies of free vibrations calculated by means of both methods were compared in [1]. This paper presents a comparison of results calculated with those from experimental measurements. A short characteristic of the equipment used, the results of measurements and some analysis are presented as well.
