ISESP XVII
Kyoto, Japan, 2024
28 October 2024 (Day 1)
ESP School
ESP Fundamentals
Dry and Wet ESPs and their Applications
Option for ESP-Upgrades
Safety and Risk Management in an Electrostatic Precipitator
ESP Modelling, Sizing, Power sources, Operations and Maintenance
Non-thermal Plasma Fundamentals and Applications
Multiple Pollutants Emission Control and CO2 Issues
29 October 2024 (Day 2)
Technical Sessions
Session 1 “Industrial ESP experience and case studies”
Low Emission ESPs for 2x1100MW Coal-fired Boilers
This paper presents one of the most advanced electrostatic precipitators (ESPs) for 2x1100MW coal-fired power boilers. For each boiler, the ESP was designed with 2x3x5 of bus sections, double high-voltage electrodes, front and back sections and 60 of three-phase rectifier transformers (TRs). Its inlet ash load, specific collection area and flue gas temperature are about 35g/m3, 136 m2/m3/s and 90-120℃, respectively. Its outlet ash concentration is around 5-7mg/m3, always less than 10mg/m3, and the ratio of PM2.5 over PM10 at the outlet is close to 10%.
The transition to renewable energy sources and the simultaneous phase-out of coal presents a significant challenge for grid stability. To ensure a secure energy supply, many aging coal-fired power plants are being repurposed as grid stability reserves. These plants must be ready to run at full capacity on short notice, potentially for only a few hours per year, while adhering to stringent environmental regulations. The Electrostatic Precipitator (ESP) is a critical component in meeting emission standards, often operating at its design limits. This paper examines a case study of an ESP plant in a German power plant built in the late 1960s, now transitioning into a grid-reserve role for the next seven years. The study involved a comprehensive analysis of operational conditions, mechanical and electrical status, and the implementation of cost-effective upgrade measures to extend the plant's lifespan and ensure compliance. The findings and methodology presented in this paper can be applied to similar plants worldwide, offering a modular approach to ESP upgrades that can be tailored to meet specific emission requirements.
Enhanced Emission Reduction: Dual Flue Gas Conditioning's Impact on Mercury and Particulate Capture
The global push for stricter environmental regulations has intensified the need for advanced emission control technologies. Electrostatic precipitators (ESPs) are challenged by high fly ash resistivity and adverse ash chemistries, particularly when dealing with coals from regions like China, India, Australia, Russia, and South Africa. Traditionally, sulfur trioxide (SO3) injection has been employed to manage high-resistivity fly ash. However, the nuanced interactions between ash chemistry, SO3, and now ammonia (NH3) injection present new opportunities for emission mitigation.
This paper explores the Dual Flue Gas Conditioning (DFGC) system, which employs simultaneous SO3 and NH3 injection upstream of ESPs to optimize particulate matter capture and significantly enhance mercury emissions reduction. The DFGC system leverages the interaction between these gases to improve the efficiency of both ESPs and mercury capture by addressing competitive absorption phenomena on activated carbon sites. Through case studies and numerical modeling, this study highlights the system's efficacy in installations across diverse coal-fired units, demonstrating how DFGC can achieve particulate and mercury emission limits previously unattainable with traditional methods.
The findings underscore the importance of understanding the complex dynamics between SO3, NH3, and activated carbon interactions. Strategic adjustments in flue gas conditioning, alongside innovative activated carbon formulations, pave the way for significant improvements in emissions control. This paper presents an in-depth analysis of these interactions and outlines strategies for optimizing mercury and particulate emissions reduction, offering a promising avenue for compliance utilizing evolving technologies. The results indicate that DFGC can be a cost-effective and scalable solution for meeting stringent environmental standards, providing significant benefits for industrial applications.
Grid Quality Parameter Comparison between Different ESP Power Supplies
Proper operation of an Electrostatic Precipitator (ESP) often assumes that the electrical grid within the industrial plant is stable. However, this is not always the case as there are many electrical machines connected to that local grid, often requiring power at different time intervals. This paper will analyse the grid quality parameters resulting from ESP energization, mainly focusing on the power factor, i.e. the ratio of active power to apparent power. The power factor parameter is usually presented in the datasheet for the ESP power supply at rated output power. However, an operating point exactly at rated output power is quite unusual for normal ESP power supply operation. Consequently, the paper will focus on the power factor at reduced output power, including reduced output voltage at rated current. Typical power factor curves are obtained in the R&D laboratory for a high frequency power supply of SIR type and a conventional single-phase transformer/rectifier. The results are compared and discussed. From the comparison, recommendations are proposed for the line power quality improvements and regulations for the ESP system using different types of ESP power supply. The conclusions are relevant for ESP grid system design guidelines, in terms of power cable and distribution transformer sizing.
Development of Ionic Wind Type Electrode ESP
In conventional ESPs, when the ionic wind from the discharge electrode strikes the collecting electrode plate, the backflow occurs, and the collection efficiency decreases. In particular, particles in the fine size range are greatly affected by this 'backflow of ionic wind', leading to increased re-entrainment of collected dust. Consequently, conventional ESPs require a large collection area to re-collect this and to achieve high collection efficiency. Therefore, reducing the effect of the backflow of ionic wind may enable the size reduction of the ESP. We started the development of a new electrode aimed at reducing the occurrence of this 'backflow of ionic wind'. As a result, it was confirmed that a significant improvement in collection efficiency could be achieved through the combination of a new collecting electrode with openings and a suitable discharge electrode. This combination of new electrodes is referred to as "ionic wind type electrode" in this paper. As a result of the pilot test in the laboratory and the demonstration operation in a thermal power plant using the ionic wind type electrode, it was confirmed that the collection area could be reduced by about 30-50% compared to the conventional ESP.
Session 2 “Environmental improvement technology”
Diesel engines have better fuel economy and emit less CO2 than gasoline engines. However, because their exhaust gas contains large amounts of nitrogen oxides (NOx), particulate matter (PM), and hydrocarbons (HC), aftertreatment is necessary. We use a new plasma aftertreatment method to remove PM in the exhaust gas. Particle concentrations are measured before and after plasma treatment using a scanning mobility particle sizer (SMPS) and a laser particle counter (LPC). The engine load is set to 0%, 24%, 48%, and 72% using electric heaters. The exhaust gas is diluted with N2+O2 mixed gas (O2 concentration 13%), and the mixed gas flow rate is adjusted to 5, 10, and 15 L/min. The input power of the reactor is adjusted to 100, 200, 300, and 400 W. PM removal performance is measured, and the removal efficiency is 83% or more under all conditions. At flow rates of 5 and 10 L/min, removal efficiency of 95% or more is obtained. At a flow rate of 15 L/min, 48% load and input power of 100W, removal efficiency of 95% or more is obtained. At a flow rate of 15 L/min, the removal efficiency decreases under several conditions. Under these conditions, the residence time is short due to the high flow rate. It is also considered that sufficient removal is not achieved due to the large number of particles before treatment and the low discharge power. The increase in small particles reduces the removal efficiency in the small particle size range. Since previous studies have achieved high removal efficiencies of 67% NOx and 76% HC using equipment and conditions similar to those of this device, we believe that this surface discharge electrostatic reactor can achieve highly efficient simultaneous removal of PM, NOx, and HC.
Particle Number (PN) emission from engine exhaust gas is legislated as a kind of harmful species like nitrogen oxide in Europe. These years, China, India and Japan introduced PN legislation, and this trend is getting common in the world. For the calibration of particle counters being used for exhaust measurement, electrostatic classifier has an important role extracting the certain size of particle to characterize the detection limit of devices against particle size. Aerosol charging technique is also essential to charge each particle and functionalize the classifier. Many of aerosol chargers consist of radiation source like soft X-ray and alpha particle emitter, which ionizes gas molecule and provides a lot of bipolar ions, but often the usage of these sources is limited by local authority due to safety concern, preventing the users from easy access to check their instruments. AC corona discharger is an optimum option to solve this issue and realize on site calibration of particle counter.
In this report, we install AC corona discharge ionizer instead of 241Am, alpha ray source on electrospray aerosol generator, and optimize its condition to achieve particle counter calibration without radioactive source. We also compare the calibration data between with conventional radioactive source and AC corona discharge ionizer.
Respiratory viruses such as SARS-CoV-2 and influenza A virus, can survive in the air for several hours, posing a risk of airborne transmission and cluster infection in settings. Ventilation using air cleaners is a crucial countermeasure to mitigate this risk. This study proposes a method for the detection of indoor SARS-CoV-2 and influenza A virus from different types of air cleaners including electrostatic precipitators by using the ultrasonicate process, following concentration of the ultrasonicated solution, RNA extraction, and reverse-transcription quantitative polymerase chain reaction. Three different approaches were evaluated to optimize the detection method. Among 105 filters from air cleaners collected from 10 locations in the hospital, SARS-CoV-2 was detected in samples from all locations, while influenza A virus was specifically detected in samples from the outpatient area. This optimized method allows for the visualization of respiratory viruses in indoor environments, improving public health by enabling better monitoring and control of viral transmission
Session 3 “ESP fundamentals and applications”
A two-stage type electrostatic precipitator operated by a pulsed power generator is developed for highly efficient aerosol collection. A compact and light weight inductive pulsed power generator driven by SiC-MOSFET with a diode rectifier is developed to generate a nano-second pulsed voltage superimposed on a DC bias voltage. The amplitude and pulse width of the pulsed voltage are 7.5 kV and 130 ns, respectively, and the maximum DC bias voltage is 4 kV. The pulsed voltage is applied to a plurality of wire-wire electrode to generate streamer discharges, and a DC voltage of -2 kV is applied to a plurality of plate-plate electrode used as collecting electrodes. A nebulizer is used to produce aerosol droplets which have diameters of sub-micrometers. The aerosol collection efficiency increases with increasing the DC bias voltage and reaches 100% with the DC bias voltage higher than 2.5 kV.
Agglomeration of Bipolar-charged Particles
Despite their high total mass filtration efficiency, electrostatic precipitators (ESPs) have a relatively low filtration efficiency of the submicron particles. This is due to the fact that these particles are too small to accumulate an electric charge large enough to allow their subsequent capture in an electric field of the precipitator. One solution to this problem is to agglomerate smaller particles into larger ones by means of electrostatic forces.
Our study investigates the agglomeration and electrostatic precipitation of airborne particles electrically charged in the region of dielectric barrier discharge (DBD). The experiments were conducted in a measurement chamber equipped with a Surface DBD actuator, with airflow forced through the chamber by a fan (Fig. 1). The aerosol containing the airborne particles from magnesium oxide powder was generated using the Topas SAG 410 and was introduced at the chamber inlet. Particle behavior was analyzed using optical Particle Tracking methods and a Topas LAP 322 particle size spectrometer, which sampled the air downstream of the DBD actuator.
Fig. 1. Diagram of experimental setup
The Particle Tracking method was employed to plot the trajectories of charged particles traveling in the electric field, between the collecting electrodes of the precipitator. The analysis revealed that particle trajectories are influenced by the sign of the acquired in the DBD charge, with some particles moving according to the electric field vector and others in the opposite direction, thus confirming that as the aerosol passes through the DBD region, the particles acquire charges of both signs. Fig. 2 illustrates the instantaneous velocity vectors of the particles.
Fig. 2 Motion vectors of bipolar-charged particles in the electric field
Fig. 3 Particle size distribution for various discharge voltages (f= 1kHz, Vair = 0.5 m/s)
Using a particle size analyzer, it was observed that the applied voltage significantly influences the particle size distribution downstream of the DBD actuator (Fig. 2). The peak of the size distribution shifts toward smaller particles, and the total particle count decreases with increasing voltage. Additionally, airflow structures within the electrostatic precipitator (ESP) were studied using Particle Image Velocimetry (PIV) and Computational Fluid Dynamics (CFD) methods. Our findings indicate that the filtration efficiency of the DBD-based ESP can be significantly enhanced by modifying the airflow with a dedicated flow guide, directing the flow closely through the plasma region and directly between the collecting electrodes. The ESP achieved optimal performance at applied voltages between 18 kV and 20 kV, reaching a total mass filtration efficiency of approximately 77% at an airflow rate of 63 l/min.
The ultimate aim of field-assisted additive manufacturing is to precisely disperse and control the distribution and alignment of individual micro/nanomaterials, such as short-chopped fibers (SCFs), in order to fully exploit and fine-tune their properties. A common challenge encountered in this field is the tendency for micro/nanomaterials to agglomerate and become entangled. Here we review the inspiration and development of our groundbreaking universal spatiotemporal electrified (STE) approach, which has successfully addressed the efficient separation and migration of individual constituents from agglomerated clusters in the gaseous phase. In the initial phases of our research, we employed high-pressure turbulent flow to disperse agglomerated SCFs. By integrating pneumatic disentanglement, we observed that pre-dispersed SCFs adhered to the dielectric-coated metallic plate and re-launched under various energized voltages within a parallel-plate electrostatic precipitator (ESP). The process exhibited complex operational procedures and a low collection efficiency of 47%. Building upon the observation of sporadic spark discharges during fiber re-launching, we propose an innovative approach involving periodic weak sparks and spatial electric fields for one-step dispersion. The self-generated periodic weak sparks generate electromagnetic fields and shock waves, effectively overcoming the significant frictional obstacles presented by agglomerates. Simultaneously, the established spatial electric field consistently attracts, selectively separates, and aligns the individual fibers. The STE approach showcases broad applicability and potential to unleash the full capabilities of micro/nanomaterials across various applications.
Particle removal from high temperature flue gas is extremely important for advanced coal conversion technologies. In this study, a high-temperature electrostatic precipitator (HT-ESP) was put forward to removal the particles from coal pyrolysis process. An experimental test facility was established to investigate the effects of temperature and gas medium on the discharge and dust removal performance. The results indicated that high temperatures negatively affected dust removal efficiency and energy consumption of the ESP. At 10 kV, as the temperature rose from 400°C to 600°C, the collection efficiency declined from 88.96% to 76.45%, accompanied by an increase in energy consumption from 32.82 W/(g/Nm3) to 39.54 W/(g/Nm3). Moreover, the collection efficiency of coal pyrolysis gas was lower than that of air, while the energy consumption in coal pyrolysis gas was higher than that in air. To address the issues of low dust removal efficiency and high energy consumption in HT-ESPs, the optimization method of positive polarity power supply and gas media conditioning were proposed. The results show that these two methods could effectively improve the dust removal performance of HT-ESPs. By using positive polarity power supply and gas media conditioning, the maximum collection efficiency was increased by 5.66% and 6.02% at 400 ℃, respectively.
As for the efficiency improvement of electrostatic precipitators through alteration, it is the major technical strategy to enhance the average output voltage and peak voltage of high-voltage power supply according to the analysis of Deutsch efficiency formula under the condition that the specific dust collection area of active electrostatic precipitator (ESP) remains unchanged due to the limitation of site space. In this paper, the matching between the three-phase pulse high-voltage power supply and the equivalent capacitance load and its application effect will be proved by comparative analysis of the matching of several common high-voltage power supplies under the state of equivalent capacitance load.
Session 4 “Industrial ESP experience and case studies”
Rehabilitation: Solution after Electrostatic Precipitator (ESP) Explosion
Electrostatic precipitator (ESP) explosion is one of the problems that can be faced by plant personnel during plant operation. It may happen due to excessive carbon monoxide (CO) content. At one of pulp and paper plants in Indonesia, the ESP, which is used for lime kiln application, was exploding.
A thorough ESP assessment process identifies which parts of the ESP remain in good condition and which require replacement, thereby reducing unnecessary costs and optimizing rehabilitation efforts. Post-assessment results in a structured, three-phase process to ensure cost-effective rehabilitation and restoration of ESP functionality. In the first phase, it is important to make sure that the ESP structure will not collapse. Moreover, the severely damaged discharge electrode and collecting plate need to be removed. In the second phase, internal part installation is performed to improve the ESP performance after explosion. The final phase includes the replacement of damaged structural casing and the upgrade of the spiral discharge electrode to a rigid discharge electrode (RDE) to restore the overall system. All plans and methods in each phase are discussed to match plant personnel expectations, the plant shutdown schedule, and the budget. The case study explores the process, challenges, and results of each phase, from the ESP explosion until the ESP is fully recovered and upgraded.
Session 5 “ESP fundamentals and applications” & “Environmental improvement technology”
A wet electrostatic precipitator is used to reduce fine white smoke which are generated in thermal power plants, and its collection plates are made of metallic materials. The particles captured on the collection plate are cleaned by water flow on the plate. Due to the electrostatic attraction force on a water droplet of the water film, electrostatic water droplets are formed on the surface, and sparks occur frequently so collection efficiency is decreased by the unexpected sparks. This study developed an electrostatic precipitator with novel collection plates using hydrophilic membrane to minimize the formation of the water droplet on the collection surface so electrical stability and high removal performance were achieved. White smoke removal efficiency of the metal collecting plate, sanded-metal collecting plate, and hydrophilic membrane collecting plate was compared under the same conditions. White smoke removal performance of the hydrophilic membrane electrostatic precipitator was evaluated based on applied voltage, flow velocity, white smoke concentration. White smoke was generated using an ultrasonic humidifier, and the concentration was measured by OPC based on PM10. At the flow velocity of 4m/s and a 13kV applied voltage, the electrostatic precipitator with the hydrophilic membrane removed over 95% of white smoke.
It has always been the unremitting pursuit of experts in the industry to achieve a more stable and lower emission at the outlet of electrostatic precipitators. Since 2014, the Chinese government has been fully implementing the new emission limit of 10mg/m3 for particulate matters from flue gas and dust. It has posed a severe challenge to the technical alteration of electrostatic precipitators under the flue gas working condition of alumina rotary kilns with high humidity, dust and viscosity that is neither suitable for bag dust removal, nor supported by a desulfurization system for dust removal. In this paper, the cases of successful technical alteration of electrostatic precipitators from 15 alumina rotary kilns are introduced on the condition of not increasing the system resistance and capacity expansion space, expounding that the technical bottleneck of achieving ultra-low emission of electrostatic precipitators has been broken through by means of systematic technical solutions such as flow field diversion optimization, body structure optimization, three-phase pulse high-voltage power supply, integrated high & low-voltage coordinated rapping control strategy and remote online real-time monitoring management on the basis of traditional electrostatic precipitators, which has achieved a good application effect and greatly improved the market competitiveness of electrostatic precipitators in terms of ultra-low emission application.
Session 6 “Environmental improvement technology”
PM Collection Characteristics using Magnetic Fluid and DC Electrostatic Force
Air pollution caused by aerosols containing particulate matter (PM) is a worldwide issue. To collect the aerosols there are high-efficiency particulate air filters (HEPA filters) and electrostatic precipitators with high collection rates. Aerosols include yellow dust, pollen, and PMs generated when fuel is burned. Carbon-based combustion PMs have high electrical conductivity and cannot be collected by electrostatic precipitators due to re-entrainment. Therefore, there is a need for a high-performance air-purifying device that can collect a variety of fine PMs, has low pressure loss, and has a high collection rate. To achieve these objectives, a magnetic fluid (MF) filter is developed. The MF filter uses MF as a collecting electrode. The MF filter collects PMs using electrostatic force, Brownian diffusion, inertial force, and gravity. It can prevent carbon-based PMs from being re-entrained due to the surface tension of the MF. In this paper, we describe the collection principle of the MF filter and the evaluation method of the PM collection rate using high-voltage DC power. In addition, the PM collection mechanism is clarified through experiments, including the performance of the MF filter.
On-line Capture of Mercury in Coal-fired Power Plants Using High Surface Energy Fly Ash
Coal-fired power plants represent the largest source of mercury emissions worldwide. Using fly ash, a by-product of these plants, as a sorbent to remove mercury has proven to be difficult. Here we found that the fresh surface of modified fly ash has good adsorption performance, and it declines obviously with time because of unsaturation characteristics on surface. Based on this mechanism, our study provides a method to on-line modified fly ash and capture mercury with high surface energy fly ash by mechanochemical and bromide treatment. Fresh modified fly ash with active sites is injected into the flue to directly adsorb mercury. A continuous system within a full-scale 300 MWe plant showed that the mercury adsorption performance of the modified fly ash is similar to that of activated carbon, mercury concentration at the ESP outlet decreases from 3.5 to 0.8 ug/m3 after the modified fly ash or AC sorbent injection and adsorption. In a full-scale 1000 MWe coal-fired power plant unit, injection of the bromide and mechanical modified fly ash resulted in a decrease of the total concentration of mercury emissions at the stack, with a mercury emission reduction efficiency of 56.1%.
Effect of Discharge Polarity on Water Treatment using DC Corona Discharge
A corona discharge was generated over an aqueous solution under varying polarity conditions to examine the influence of water treatment on discharge polarity. The discharge was produced 4 mm above the water’s surface. The experimental solution, an aqueous acetic acid solution adjusted to pH 7.5 with sodium hydroxide, served as a model for persistent organic compounds. The concentration of acetic acid in these tests was approximately 25 mg/L. Positive ions flowed into the liquid surface under positive polarity, while negative ions did so under negative polarity. The applied voltage and discharge current were 5.70 kV and 0.730 mA for positive polarity, and 5.55 kV and 0.745 mA for negative polarity, respectively. Post-treatment measurements indicated higher concentrations of dissolved ozone and hydrogen peroxide under positive polarity. Conversely, the decomposition rate of acetic acid was higher under negative polarity. These findings demonstrate that ion species supplied during DC corona discharge significantly impact acetic acid decomposition.
Poster Session
“ESP fundamentals and applications”
Effect of Applied Voltage in an Electrostatic Precipitator with Airflow and Electrostatic Force
It is important for the collection efficiency of an electrostatic precipitator understanding that the relationship of electric field and gas flow distributions. Because, the gas flow is resistant for migrate of the charged particles to collecting electrode. Aim of this study is that the particle removal efficiency is improved with gas flow. Hence, the gas flow is suctioned the gas near the collecting electrode. This effect is considered that the collected particles are difficult to accumulate on collecting electrode, therefore the time period for cleaning collecting electrode expand. The diagram of experimental apparatus is shown in Fig.1. This present version electrostatic precipitator was consisted of precharger and particle removal section. Precharger was used a positive corona discharge. The particle removal section was coaxial cylinder configuration, the center electrode applied negative high voltage, and the outer electrode was grounded. If the assumption is correct, the charged particles are attracted near the center electrode. The gas near the center electrode was suctioned at downstream of center electrode. As results, particle removal efficiency improved with drawing gas by suction. The particle concentrations in suction gas will be measured for various applied voltage.
Heavy metals that adhere to suspended particles can cause oxidative stress in humans. Copper is an air pollutant that attaches to particles. A wet-type electrostatic precipitator to precipitate copper from the collected particles onto the collecting electrode is proposed in this study. Wood ceramics are used as the particle collection electrodes. Wood ceramics were made of sawdust and phenol resin powders formed by vacuum sintering. Woodceramics electrode is conductive porous media that contain water. The migration of copper under corona discharge was tested using a nitrate copper solution contained in a chromatography paper instead of the collected particles. In this study, wet wood ceramics were used as the grounded electrodes. The influence of atmospheric humidity on corona discharge was tested. The weight of the copper was measured using an atomic absorption spectrometer. It is confirmed that copper movement decreases as the humidity increases. The movement of copper is caused by the difference in the polarity of the corona discharge. A tendency for the copper weight to increase when treated with a negative corona discharge was observed. Nevertheless, the weight of copper did not change under a positive corona discharge.
Effect of Pulse Discharge Polarity on Aerosol Collection
The effect of the polarity of the nanosecond pulse discharge on the aerosol collection efficiency was investigated. An Inductive Energy Storage (IES) pulse power supply was used to generate nanosecond pulse discharge. A pulse voltage of 11 kV was applied to the discharge section and a DC voltage of 2 kV was applied to the electrostatic section. Air was injected into the Electrostatic Precipitators (ESPs) by a compressor at a gas flow velocity of 1.0 m/s. Tap water was nebulized and mixed with the gas flow. The water particle concentration for the particle size between 0.3 and 5 μm was measured to calculate the collection efficiency. The results showed that the collection efficiency was higher and the energy consumption was lower when a negative polarity pulse voltage was applied than when a positive polarity pulse voltage was applied. These results indicate that high dust collection efficiency with low energy consumption can be achieved by applying a negative polarity pulse voltage to the discharge section.
“Industrial ESP experience and case studies”
The principle of dust escape from the outlet groove plate of the electrostatic precipitator (ESP) was analyzed, and the pneumatic vibration ESP technology for small units of groove plate (SQ-ESP) was developed. By dividing the outlet groove plate of the ESP into small units and setting up a separate vibration for dust removal, its dust collection function was achieved and the bottleneck of secondary dust lifting technology affecting the ESP was solved, achieving the goal of improving the efficiency of the ESP. In December 2023, the ESP of a 630 MW unit in a power plant in Jiangsu Province was renovated and subjected to engineering application tests. The performance was compared under different load using the coal which is difficult to electrostatic precipitator. The test results showed that under full load, the dust concentration at the outlet of the ESP decreased from 25.3-28.6 mg·m-3 before the renovation to 15.0 mg·m-3 after the renovation, and the efficiency of the ESP was significantly improved.
The ESP characteristics of 16 kinds of Vietnamese coal smoke and dust are counted and compared with 51 kinds of China coal. It finds that the Na2O content of Vietnamese coal ash is significantly low and resulting in poor ESP performance. A comparison is made between the emission indicators of coal-fired flue gas and dust at home and abroad, and it find that the Vietnamese standard requirements are relatively low. The selection and design of the ESPs for the Yongxin project in Vietnam are carried out. After the project is put into operation, the performance of the project is tested and compared. The results shows that the core components of the ESP, which were produced in China, could achieve an export dust concentration of 30.2 mg·m-3 and a dust removal efficiency of 99.93%, far superior to the owner's requirement of 98 mg·m-3 and Vietnam 200 mg·m-3 Emission standards when burning low-quality Vietnamese coal, which have the advantages of compact structure, low cost, and great potential for international market promotion.
Study of Electrostatic Precipitator in Large Scale Carbonizing Furnaces
The purpose of this study was to investigate an electrostatic precipitator for collecting dust and dirt generated during the combustion of organic waste. A prototype precipitator was fabricated for testing in the experiments. The electrodes were wedge and flat-plate types, and the electrode spacing was set to 7 mm. A Cockcroft–Walton circuit and cold cathode tube inverter were used for the high-voltage generator circuit. Current–voltage and dust collection measurements were conducted using a reduced-scale prototype electrostatic precipitator. Consequently, the dust collection efficiency was limited to a few percent, which is considered extremely low for practical applications. However, the dust collection efficiency for PM2.5 and PM10 was found to be over 90% after re-measurement with a limited particle size.
The article presents the results of a research on conditioning flue gases in front of an electrostatic precipitator (ESP) and on reducing mercury emissions from coal combustion by injecting a selected oxidant into exhaust gases and/or by feeding an additive stabilizing mercury compounds present in the sorption solution into the circuit of wet flue gas desulphurization (WFGD) absorber. Based on experience from the research conducted in industrial conditions, a multi-variant and low-cost technology has been developed that allows achieving the expected level of mercury emission reduction using existing air pollution control systems (APCS) (e.g. electrostatic precipitator, WFGD absorber). However, each time interaction of subsequent devices/installations through which contaminated exhaust gases flow should be taken into account. For example, excessively high dust concentration behind the electrostatic precipitator causes problems in the operation of the WFGD installation, resulting in a deterioration of quality of the synthetic gypsum produced. The results of the described research additionally confirmed that excessively high dust concentration (at the level of 150 mg/m3ref) does not allow achieving the desired mercury concentrations in the emitter, which result from the BAT conclusions.
“Numerical simulation for ESP modelling”
The purpose of this study is to investigate the effect of nanosecond pulsed corona discharge with DC bias on particle trajectory in a wire-to-plate type electrostatic precipitator (ESP). The simulation was performed using COMSOL Multiphysics🄬 (Ver. 6.2) to calculate the electric distribution and the space charge density. The experiment was carried out using particle image velocimetry (PIV) to measure the particle trajectory in the ESP, and to be compared to the simulation.
As a result of the simulation, the negative ions were flowed to downstream side of the wire electrode due to the pause period in the voltage at the nanosecond pulsed corona discharge without DC bias. However, since the electric field was constantly generated at that with DC bias, the negative ions were spread to the area between the wire electrode and grounded electrode. In the experimental result, it was shown that particles migrated to the grounded electrode at the nanosecond pulsed corona discharge with DC bias, while particles were flowed to the downstream side at that without
DC bias.
Durability of Brush Electrode in an Electrostatic Precipitator
An electrostatic precipitator (ESP) is suitable for collecting nano-order suspended particles. In order to clean the air in living spaces using ESPs, a low ozone concentration must be maintained. Therefore, the aim of this study is to investigate discharge electrodes that can achieve high collection efficiency for long periods of time at low ozone concentrations. In this study, the durability performance of a disk-shaped carbon brush electrode in long-term operation was investigated in positive and negative corona discharges. The ESP consisted of a discharge section, which had a disk electrode with 20 carbon brushes, and an electrostatic section. A positive or negative DC high voltage was applied to the discharge section and the ozone concentration was adjusted to 0.05 ppm, and the ESP was operated for 2,000 hours. Initially, the collection efficiency under negative corona discharge was 94%, and decreased to 83.6% after 2,000 hours. Conversely, under positive polarity, the initial collection efficiency was 99.5% and remained high at 94% after 2,000 hours. This indicates that positive polarity can maintain high collection efficiency over 2,000 hours under low ozone concentrations.
“New ESP technique” & “Particle and aerosol charging”
In this study, experiments were carried out to improve the collection efficiency and increase the gas velocity in a high electric field type electrostatic precipitator (ESP), which was the ESP for energy saving. The ESP was a coaxial cylinder structure, which was composed of a grounded cylindrical electrode and a high voltage application columnar electrode, with the gap distance of 6.1 or 10 mm, and the electrode length was 470 mm or 2000 mm. The negative DC high voltage up to 19 kV was applied to the columnar electrode. As no discharge current was detected, whose measurement accuracy was 0.01mA, the power consumption was less than 0.19 W. A diesel exhaust gas was flowed into the ESP at the gas velocity of between 1 m/s and 8 m/s. The particle mass concentrations were measured with/without applying high voltage using a low volume air sampler. And the collection efficiency was calculated. As a result, the collection efficiency at the gas velocity of 8 m/s achieved 89% without energy consumption
This paper describes the treatment of carbon particles, which is one of the environmental problems. The authors have developed a technology to capture and decompose carbon particles using a dielectric barrier discharge. In this technology, carbon particles are captured on a substrate for surface dielectric barrier discharge (SDBD) and then incinerated by low- temperature plasma generated by SDBD on the substrate. This study focuses on the decomposition process. A sub-electrode was installed on the SDBD plate in addition to the main electrode to which a voltage is applied, and the CB decomposition characteristics were compared using the following three connection methods between the main electrode and the sub-electrode: (1) a connection method in which the sub-electrode is not connected to the surrounding conductor and has a floating potential, (2) a connection method in which an external inductor (Le = 1.07 H) and a capacitor (Ce = 50, 100 pF) are attached, and (3) a connection method in which the same voltage as the main electrode is applied to the sub-electrode. The following results were obtained from a decomposition experiment of carbon black (CB) applied on a substrate as a simulant of exhaust gas soot. In terms of the relationship between power consumption and the reduction ratio of fine particles on the surface, connection method (1) was the best, but the decomposition area was limited to the vicinity of the main electrode. On the other hand, method (2) of adding an external LC achieved more uniform decomposition on the area between the main and sub-electrodes. As for (3), CB near the middle of the gap between the main and sub-electrodes could not be decomposed at all.
Development of Compact Electrostatic Precipitator using EHD Gas Pump Mechanism
In recent years, the removal of airborne particulate matter, such as PM2.5, pollen, and droplets containing coronavirus, has become an increasingly important issue. Collecting dust closer to its source is considered more effective for removing these particulates. However, most air purifiers are stationary devices, and electrostatic precipitators (ESPs) that can move freely, like a robotic cleaner, have not yet been developed. In this study, we have developed a compact, lightweight electrostatic precipitator (ESP) capable of moving to the source of dust for collection. To eliminate the need for an electric fan to draw particles into the ESP, we employed the mechanism of an electrohydrodynamic (EHD) gas pump, which uses ionic wind. A wire-to-non-parallel plates electrode configuration was used to generate unidirectional gas flow containing dust particles. This configuration allows for the simultaneous corona charging of particles and their precipitation onto the plate electrode. The performance of this single-stage compact ESP was evaluated through visualizations of dust particle collection in a transparent acrylic chamber and a mini plastic greenhouse. The proposed compact ESP has no mechanical moving parts and can be integrated into mobile devices or combined with other units.
“Air purification, Advanced oxidation process”
Highly-efficient Plasma Oxidation of N-undecane over Co-doped CeO2
n-Undecane (C11) is a typical alkane pollutant, accounting for 6% of the total volatile organic compounds (VOCs) emitted from the printing industry in China. Here, we report that C11 is efficiently removed using plasma catalytic oxidation with a Co-doped CeO2 catalyst prepared by aerosol decomposition method which can take advantages of doping, nano engineering, and interfacing. C11 conversion and COx selectivity were as high as 100% and 97%, respectively, when a plasma catalyst reactor was operated at 100 °C and 30 J/L for treating a gas mixture containing 265 mg/m3 C11 at a weight hourly space velocity of 13700 mL/g/h. The influences of gas temperature, C11 concentration, energy density, and water have been investigated. The catalyst characterization results show that higher Ce3+/(Ce3++Ce4+) and Co3+/(Co2++Co3+) ratios are beneficial to C11 oxidation. An operando plasma diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to explore the mechanism of C11 decomposition.
“Environmental improvement technology”
Continuous Ambient Air Dust Analysis and Assessment System for Air Quality
Dust in air, widely known also PM (Particulate Matter), has attracted a lot of attention from scientists since people breathe air with dust in their vital functions and the impact on health from it specifically to lungs is reported as high. Dust is not only artificially but naturally generated in ambient air, and therefore it is difficult to control its concentration. Capturing the shift of pollutants and tracing their source will be a next stage on ambient air monitoring because the current guideline is based on steady-state environment condition with long term. Harmful inorganic metals in dust stay mostly stable in transition with long distance. Continuous monitoring with analysis of the features is one of the most effective ways of retaining ambient environment healthy.
In this report, we suggest a comprehensive system for assessment of ambient air dust by the cycle of analysis, countermeasures, verification, and continuous monitoring. We have developed the following 4 key technologies in order to achieve the assessment: 1) Dust analyzer with combination of beta-ray attenuation and X-ray fluorescent techniques, 2) Diluter for application to stack monitoring beyond ambient air fields, 3) Data acquirement software, and 4) Data processing method for source apportionment.
Characteristics of Hydrogen Peroxide Production by Diaphragm Discharge Plasma
Plasma/ozone combination processes using a diaphragm discharge plasma as an H2O2 source were performed to decompose acetic acid in water. A higher decomposition rate was obtained at a higher solution temperature. It was confirmed that the H2O2 production rate starts to decrease when the solution temperature reaches 70°C but there was no large difference under 70°C. Therefore, the reason of the higher decomposition rate was due to the enhancement of reactions in water.
The ammonia-coal co-firing for thermal power generation has recently been attracting attention because ammonia (NH3) does not emit carbon dioxide (CO2) during combustion. However, there is concern that the amount of nitrogen oxides (NOx) emitted during combustion will increase compared to coal-fired combustion because NH3 contains N components, and there is a need to develop a NOx treatment method with a higher removal efficiency. Therefore, we propose plasma chemical hybrid process (PCHP) as an NOx removal technology that can be added to existing exhaust gas treatment equipment. In this study, we conducted NOx oxidation experiments in the presence of low concentrations of NOx and high concentrations of SO2, and simultaneous removal experiments of NOx and sulfur oxides (SOx) on a laboratory scale to understand the basic characteristics. As a result, it had sufficient oxidizing performance to introduce PCHP, and it was also possible to remove NOx and SOx simultaneously. Further NOx removal is possible by adding PCHP to the exhaust gas treatment flow in thermal power generation.
“Bacteria elimination/inactivation/bio & organism-related technologies”
High-voltage Pulse Inactivation of Bacteria in Frozen Water and Orange Juice
In recent years, the demand for frozen foods has increased. Freezing food can suppress reactions that degrade food quality, such as microbial spoilage, thereby preserving its quality. While microbial activity stops during frozen storage, bacteria can proliferate upon thawing. If PEF pasteurization proves effective for frozen suspensions of Escherichia coli, it can be expected to sterilize the food without thawing. A PEF treatment chamber utilizing modified electroporation cuvettes with a 2 mm electrode gap was employed. PEF treatment was conducted on frozen samples at -15℃ within a freezer. The PEF treatment involved applying a voltage of 5 kV with a frequency of 50 pps. As PEF pasteurization of frozen distilled water and orange juice, the pasteurizing effect improves as the PEF treatment time increases, and both can be sterilized to N.D. (undetectable) with a treatment time of 140 min. It was confirmed that PEF sterilization is effective for frozen E. coli suspended distilled water and orange juice. Elucidation of the inactivating mechanism of bacteria by applying PEF at low temperatures is a topic for future study. In an investigation of the total sugar content and reducing sugar content of mandarin orange juice when PEF was applied, it was confirmed that PEF treatment had no effect on each sugar content.
“Bio-aerosol collection”
Inactivation of Airborne Viruses in an Electrostatic Precipitator with Deep Ultraviolet LED
In this study, the inactivation effect of an electrostatic precipitator (ESP) and a deep ultraviolet (UV) LED was investigated. The experimental system consisted of an ESP and a UV irradiation part. The ESP was composed of a precharger and a collector. The UV irradiation part was installed at the downstream side of the ESP. The positive DC high voltage was applied to the precharger and the collector. The air included viruses was flowed into the ESP with UV irradiation part at the velocity of between 0.1 m/s and 0.5 m/s. MS2 phage was used as airborne viruses. The collection efficiency and the inactivation effect on collected viruses and airborne viruses were measured using a plague assay method. As a result, the collection efficiency of 99% was achieved in the ESP. The survival ratio on the collection electrode decreased to between -1.4 log10 and -2.9 log10 for 4 min by UV irradiation. The survival ratio in the air decreased with increasing the UV dose. The survival ratio of -2.1 log10 was achieved at the UV dose of 7.1 mJ/cm2, whose exposure time was 4.8 s.
“Applied electrostatics & non-thermal plasma”
We developed a new annular electrode arrangement for the surface resistance measurement on insulating material. A pair of annular electrodes is located on each side of a flat surface of plate specimen. In the new electrode arrangement, the current flows almost along the surface, which was confirmed by FEM of 3D configuration model. In the conventional electrode arrangement of IEC 62631-3-2, on the other hand, the current from the inner electrode flows almost in the bulk of the insulating materials due to the existence of the backside electrode. The current measured with the new arrangement is almost 10 times larger than that with the conventional arrangement. In our FEM model, elements are composed with totally 6 layers, which is composed with 2 surface layers and 4 bulk layers. The volume resistivity used for the calculation was obtained by the measurements with specimens, epoxy resin and Phenoric resin. The surface current obtained by the measurement was one order larger than the current obtained by the FEM when the volume resistivity of surface layer and that of the bulk layer are the same value. FEM calculation indicates that the calculated current matches with the measured current with epoxy resin specimen when the volume resistivity of 1 nm thick surface layer is assumed to be seven orders smaller than that of the bulk. In the case of 1 nm thick , the resistivity of surface layer is estimated to be 3ｘ106 Ω·m..
We developed a new annular electrode arrangement for the surface resistance measurement on insulating material. A pair of annular electrodes is located on each side of a flat surface of plate specimen. In the new electrode arrangement, the current flows almost along the surface, which was confirmed by FEM of 3D configuration model. In the conventional electrode arrangement of IEC 62631-3-2, on the other hand, the current from the inner electrode flows almost in the bulk of the insulating materials due to the existence of the backside electrode. The current measured with the new arrangement is almost 10 times larger than that with the conventional arrangement. In our FEM model, elements are composed with totally 6 layers, which is composed with 2 surface layers and 4 bulk layers. The volume resistivity used for the calculation was obtained by the measurements with specimens, epoxy resin and Phenoric resin. The surface current obtained by the measurement was one order larger than the current obtained by the FEM when the volume resistivity of surface layer and that of the bulk layer are the same value. FEM calculation indicates that the calculated current matches with the measured current with epoxy resin specimen when the volume resistivity of 1 nm thick surface layer is assumed to be seven orders smaller than that of the bulk. In the case of 1 nm thick , the resistivity of surface layer is estimated to be 3ｘ106 Ω·m..
Adhesion Improvement of Fluoropolymers by Atmospheric Plasma Treatment
Fluoropolymers are attracting attention as a material for medical devices and high-frequency circuit boards. But it is difficult to adhere them to other materials due to their chemical stability. In this study, the adhesion of fluoropolymers was improved by atmospheric plasma treatment. The target of the treatment was polytetrafluoroethylene (PTFE). The adhesive strength was 2.7 times higher than that of the untreated material by the oxygen plasma treatment. Furthermore, it was decreased from 103˚ before the treatment to 53˚ after the oxygen plasma treatment, indicating a high hydrophilic effect. This is thought to be due to the substitution of fluorine groups for hydrophilic groups by reactive species such as ozone (O3) or hydrogen peroxide (H2O2). Then, the contact angle was decreased to 36˚ by the addition of 1% hydrogen to the oxygen plasma, resulting in higher hydrophilicity. This is thought to be due to increased substitution of hydroxy groups (-OH) and other hydrophilic groups, resulting in an increase in hydrogen-derived reactive species.
Effect of Ratio of Wood Biomass and Air in Non-Thermal Plasma Reactor on Generation Gases
The biomass power generation is one of applications using biomass. However, for example, thermal efficiency of law wood burning is not high. Therefore, it is important that the conversion technology to useful fuel and high efficiency energy material from biomass resources. The aim of this study, the new conversion technology is proposed that the sawdust treated with non-thermal plasma to generate gas fuel. A schematic diagram of experimental apparatus is shown in Fig.1. Volume 20 ml of the vial bottle was use as plasma reactor. High voltage wire electrode was set into the bottle and grounded electrode was pasted outside of the bottle. Dielectric barrier discharge was generated on inside bottle wall. The saw-dust and room-air closed in bottle, both treated with non-thermal plasma simultaneously. After treatment, gases were evaluated with FT-IR. As results, CO, CO2 and CH4 were observed. We focused on the ratio of sawdust and air in the reactor. The volume ratio 2 sawdust and 1 air was the most generated methane in this test condition. On the other hand, the influence of moisture of saw-dust to generate methane is known in past research. Therefore, the volume ratio of sawdust and air, and moisture of sawdust will be evaluated.
349 mm Linear Type Atmospheric Remote Plasma Source for Large Area Surface Treatment
In recent years, atmospheric low-temperature plasma has been widely used for surface treatment. In our laboratory, an atmospheric pressure multi-gas plasma jet source, which can generate low-temperature plasma with various gas species, has been developed. However, two-dimensional scanning is required to treat large area, since the diameter of the plasma injection hole of this device is 1 mm. In this study, to treat large area with one-dimensional scanning, a new linear type atmospheric remote plasma source was developed. This plasma source has a plasma irradiation slit of 1 mm x 349 mm and low-temperature plasma is emitted like a gas curtain. Stable plasma could be generated with argon, helium, nitrogen- argon, oxygen-argon, and carbon dioxide-argon by applying a radio frequency of 13.56 MHz to the electrodes and flowing a plasma generating gas at a rate of 20 L/min. To evaluate the characteristics of this plasma source, water contact angle was measured at 15 equally spaced points on the sample irradiated with plasma from the slit. As a result, in the case of mixing 2.0% nitrogen to argon plasma treatment, contact angle decreased 14 degrees more than argon plasma treatment at all measurement points. Furthermore, by applying 500 W of RF power, dispersion at the 15 measurement points got 5.8 times lower than applying 200 W. It means uniform hydrophilic effect was obtained over large area.
Simultaneous Removal of VOCs and Nanoparticles using a Wet-type Catalytic Nonthermal Plasma Reactor
Atmospheric pollutants due to volatile organic compounds (VOCs) have become a societal issue, leading to the implementation of various emission regulations. Emissions from paint and printing factories contain VOCs that produce photochemical oxidants and particulate matter, such as PM2.5, contributing to global environmental problems. Nonthermal plasma (NTP) technology offers efficient removal of various harmful atmospheric pollutants compared to traditional methods. NTP possesses clear advantages, including the absence of maintenance requirements, low operational costs, and wide applicability at room temperature and atmospheric pressure. In this study, we propose a plasma reactor with a wet catalytic layer filled with α-alumina using a water film. The wet-catalyst NTP reactor possesses advantages for VOC control, such as activated catalyst, high energy efficiency, utilization of highly reactive species like O or OH radicals, conversion to water-soluble byproducts, and removal of byproducts by water flow. Initial evaluation of the proposed technique involves simultaneous removal of nanoparticles along with individual VOCs. As results of nanoparticle collection during the VOC treatment, the average particle collection efficiencies show above 98%. Furthermore, the treatment achieves the removal efficiency of 73%, 100%, 100%, and 95% for toluene, acetaldehyde, acetic acid, and ammonia, respectively.
“Plasma fundamental & diagnostics”
We measured the time evolution and spatial distribution of electron energy distribution function (EEDF) in an atmospheric-pressure air streamer discharge using laser Thomson scattering (LTS). We generated single-filament 2 Hz high-voltage positive pulsed streamer discharge with high spatiotemporal reproducibility in a 13 mm needle-to-plate electrode gap. To improve the signal-to-noise ratio, the LTS signal from 4,000 laser shots were accumulated. The rotational Raman scattering (RRS) signal from N2 and O2 in air, which was about 20 times larger than the LTS signal from electrons, was subtracted from the superimposed RRS+LTS signal. At 3 mm below the anode needle tip, LTS signal intensity gradually decreased with the reduction in streamer optical emission. By comparison with EEDFs calculated using the Boltzmann equation, a small peak signal was observed at high-energy region. The small peak signal was identified as an RRS change caused by 10-15 K increase in gas temperature ∆Tg. The measured EEDFs at 10 mm, where the streamer optical emission has not reached, showed reduced electric field E/N and electron density ne, with no observed change in gas temperature.
Atmospheric pressure plasma jet’s interaction to solid and/or liquid targets is one of the concerns in medical, mechanical, and biological applications. When the interaction of plasma jet is considered based on energetic point of view, the form and transportation of electrical energy throughout from the breakdown of atmospheric gas to the interaction with target’s surface change in time and space. The electrical energy at the moment of breakdown is consumed for immediate local heating and plasma emission, then, followed by the generation of shockwave in gas. The shockwave is degenerated with distance in the plasma jet tube and emitted outside of the tube, arriving at target’s surface as pressure wave. Therefore, the measurement of pressure wave at the location of targets is important to understand plasma-target interactions, however, it can not be detectable in conventional optical methods due to the interruption of jet gas flow and their insufficient sensitivities. A unique optical technique called optical wave microphone, which has been developed by the authors, works based on the Fraunhofer diffraction of laser for phase objects and it had successfully detected pressure wave emitted by helium and argon plasma jet at the downstream of the plasma jet. In this work, a fiber type optical wave microphone and a high-speed camera were used for synchronized investigation of pressure wave influence on plasma-induced flow caused by plasma jet. The plasma induced flow was investigated with KI-starch method. According to the experimental results, the amplitude of pressure wave was strongly related to the fluctuation of plasma jet and plasma induced flow.
30 October 2024 (Day 3)
Technical Sessions
Session 7 “Industrial ESP experience and case studies” & “New ESP technique”
Development and Implementation of Custom ESP Profile on ZigBee Protocol for Industrial Applications
This paper describes the development of custom Electrostatic Precipitator (ESP) profile on top of ZigBee wireless protocol for industrial applications. This profile has been implemented for control and monitoring of ESP functionalities in a thermal power plant. This wireless protocol has replaced the already existing wired or cabled controls between the control room and field, thus optimizing the resources or materials required for commissioning. The custom profile is developed considering the maximum number of parameters to be monitored and controlled in ESP in a thermal power plant. The profile can co-exist with multiple networks of same profile and ensures ease of troubleshooting and maintenance with the help of various indications in the hardware. This wireless profile is deployed in various thermal power plants for ESP control application and has proved to be reliable. This can be extended to other areas of the power plant to bring the entire power plant under a single ZigBee network. The field data and the node status can be viewed at a centralized point or even a handheld device.
The Application of Electrostatic Precipitators in the Pulp & Paper Plants
Achieving low emissions in kraft recovery boiler operations is essential for pulp and paper plants in China, particularly in greenfield installations equipped with new electrostatic precipitators (ESPs). This article explores the critical design and operational factors that contribute to the sustained high performance of ESPs in minimizing particulate emissions. Key variables impacting ESP efficiency include ash composition, flue gas conditions, and specific design parameters. We delve into the roles of electrical resistivity, temperature, moisture content, and particulate concentration in optimizing ESP performance. Special attention is given to the influence of chloride content in ash, which significantly affects ESP capture efficiency. Additionally, we discuss design considerations such as electrode configuration, gas flow distribution, and advanced power supply systems that enhance ESP effectiveness. By understanding and integrating these critical factors into the design and operation of new recovery boilers, pulp and paper plants in China can achieve and maintain exceptionally low particulate emissions, ensuring compliance with stringent environmental standards while optimizing operational efficiency. This article provides a comprehensive guide for industry professionals involved in the design and implementation of high-performance ESPs in recovery boilers for the Chinese market.
This study designed and tested a novel wet electrostatic precipitators (WEP) system featuring a Pulse-Air-Jet-Assisted Water Flow (PJWF) to shorten water cleaning time, reduce water usage, and maintain high particle removal efficiency. The PJWF injected cleaning water tangentially at the cylinder wall, rapidly enhancing the momentum of the water flow for efficient dust cake removal. Each PJWF cycle uses approximately 4.8 liters of cleaning water in 18 seconds. Comprehensive laboratory tests were conducted using a single-tube WEP prototype within a flow rate range of 3.0 to 6.0 cubic meters per minute(CMM), operating voltages between -35 to -55 kV, and high-frequency power supply. The prototype, consisting of 72 sets of double-spike rigid discharge electrodes, demonstrated that with the PJWF, -35 kV, and 3.0 CMM, the PM2.5 collection efficiency remained as high as the initial value of 88.02±0.92% after loading with Al2O3 particles at 35.75± 2.54 mg/Nm3 for 20-hr continuous operation. In contrast, without the PJWF, the PM2.5 collection efficiency drastically dropped from 87.4% to 53.5%. Theoretical modeling closely matched experimental results, confirming the robustness of the system's design and its scalability for larger industrial applications. Future research will focus on optimizing the PJWF system, exploring its performance with various particulate matter, and ensuring long-term operational stability and reliability under diverse environmental conditions.
The ESP (Electrostatic precipitator) of a 54 MW power boiler at a petrochemical plant in Thailand, commissioned in 2000, initially operated below its design capacity due to high emission levels, measuring 288 mg/Nm3 against a designated limit of 300 mg/Nm3. To comply with stringent emission regulations and mitigate environmental impact, an upgrade of the existing ESP was necessary despite spatial constraints. The upgrade involved replacing the traditional 21 square wire type DE (Discharged electrodes) per layer with 8 (Rigid discharged electrodes) per layer, accompanied by the installation of a H/F (high frequency) transformer to lower onset voltage and enhance average electrical field strength within the ESP. The transformer output voltage was increased from 65 kV to 83 kV. Post-retrofit, particulate matter emissions decreased significantly from 288 mg/Nm3 to 108 mg/Nm3, even as inlet dust loading rose from the baseline of 2,396 mg/Nm3 to 7,301 mg/Nm3. The ESP efficiency correspondingly improved from 87.98% to 98.51%, enabling the system to operate efficiently and meet regulatory standards.
Insights into Condensing-type WESPs: Coupling Mechanism between Corona Discharge and Heat Transfer
Enhancing fine particle removal is crucial for reducing industrial emissions. This study improves WESP models by coupling corona discharge with heat transfer under phase transition. The study explores the effects of multi-field coupling on particle behavior and removal efficiency in a condensing-type WESP. Results show that the coupling induces ionic wind, linking corona discharge and heat exchange, which lowers flue gas temperature by 3.7 K at 32 kV, promoting particle growth and charge. This research advances WESP models and provides insights into condensing-type WESPs.
Design and Application on Super Large Coal-fired Power Plant Unit Electrostatic Precipitator
Large capacity, low energy consumption of coal-fired power generating units was one of the development direction in the coal-fired power generation industry at home and abroad. The 1350MW coal-fired unit electrical precipitator (ESP) in Anhui as an example, different schemes of ESP per boiler with 2 sets- 4 chambers -5 electric fields, 3 sets- 3 chambers -5 electric fields and 4 sets- 2 chambers -5 electric fields were compared and analyzed, the comparison result shows that the economic advantages of 2 sets- 4 chambers -5 electric fields was obvious in order to meet the requirements of design outlet dust concentration. The project was put into operation at the end of 2020 and the application verification was carried out from the aspects of selection design, scheme design, installation and operation. The ESP passed the 168 test successfully and the dust concentration at the outlet of the ESP was stable below 10 mg·m-3 according to the turbidity meter observation and 8.1 mg·m-3 according to on site sampling test. the resistance of the electrostatic precipitator body is 159.3 Pa, the air leakage rate of the electrostatic precipitator is 1.14%, and the air leakage rate of the main body meets the requirement of less than 2 %.The primary power consumption of the high-voltage side of the ESP was 498kW, which was much lower than the power consumption of similar advanced ESP.
Session 8 “Numerical simulation for ESP modelling” & “Industrial ESP experience and case studies”
Sumitomo Heavy Industries, Ltd. (“SHI”) has been involved in continuous research and development to improve the electrostatic precipitator (“ESP”) since the 1930s. As a result, over 500 ESPs have been delivered to various industries. During our history, with an aim of supporting our customers, SHI has been investigating performance diagnosis/forecast by using own R/D facility. Among one of these studies, the shape and array of discharge electrode is the key points to determine ESP performance. The purpose of this study is to focus on a comparison of the current density and dust collection efficiency among the different type of the discharge electrodes. This experiment has been performed in a pilot scale ESP with wire-to-plate and was carried out with different discharge electrode pitches which was constituted by 3 wires. The result showed that the narrow pitch led to fade out the current density from the middle of the wire affected by both side of one, on the other hand the pitch was wider, the better current density distribution from each wire it had not to disturb each one. Meanwhile, for the view of dust collection efficiency, the best pitch of wire was under the array admitted some interference of the current density from each wire. As a conclusion, ESP has the best performance under a proper discharge electrode pitch. To get suitable result for variety types of discharge electrodes, same examination should be conducted in accordance with the shapes of it, as SHI has already achieved to handle by this method.
A Profiled GD Screen to Improve Even Flow Distribution in Electrostatic Precipitator
Present numerical investigation discusses about the design and different arrangement of gas distribution (GD) screens inside ESP inlet funnel for uniform and even distribution of flue gas in the downstream direction. In conventional ESP’s splitters and round profiled gas distribution screens with verified deflection plates are used to correct the incoming flow disturbances which requires many trials, testing and also faces issues like erosion. To overcome this, a new method is suggested where conventional splitters are eliminated and conventional GD screens are replaced with Polygonal profiled gas distribution screens at appropriate location where there is sudden change of area ratio.
Three dimensional geometric models are developed for the new profiled GD screens and numerical simulation was conducted using CFD tools such as ANSYS workbench. The computational domain extends from outlet of Air Pre-heater to the inlet of ID Fan for simulating the flue gas flow inside the ESP. CFD analysis was carried out with different skewed flow condition at ESP inlet, along with appropriate turbulent model and physical parameters. Regardless of different kind of flow instabilities at inlet, distribution of even and uniform flow was achieved in the downstream direction. CFD tools are effectively utilized in this study to evaluate and improve the performance of the electrostatic precipitator.
Efficiency Improvement of Existing ESPs
Coal based Thermal Power Plants are backbone of Indian Power Sector which caters more than 50% power generation source in India. The aging fleet of ESPs are about 25 – 40 years old now which were designed to achieve 100 – 150 mg / Nm3 of particulate matter. Considering recent MoEF (Ministry of Environment & Forest) guidelines, ESP outlet SPM emission should be limited between the range of 17 mg / Nm3 and 50 mg / Nm3. Such units provide good opportunity for ESP R&M (Renovation & Modernization) and life extension of existing old thermal power plants.
ESP upgradation is the most important job for meeting the revised SPM emission norms as the old ESPs are designed on higher outlet SPM emission level. ESP upgradation is quite challenging, considering limited space in existing plant and un-interruption of energy generation.
K.C. Cottrell India have executed many challenging jobs of ESP upgradation of various coal based thermal power plants. Below are the project list and schemes provided to achieve desired outlet SPM emission level of ESPs:
Successfully completed all the four Power ESP R&M projects: NTPC – Badarpur, WBPDCL – Kolaghat , NTPC Farakka and Tata Power Trombay. Achieved ESP outlet SPM emission level even lower than the desired guaranteed limits. 2X500 MW Anpara TPS ESP R&M project is under execution and we hope to complete it successfully by October 2024.
Flow Optimization in Electrostatic Precipitator using Multi Phase Flow Simulation
This research clearly focuses on improving the primary flue gas flow and secondary ash particles flow at the Electrostatic Precipitator inlet. In contrast to present day practice of single phase flow simulation with primary flow alone, simulation of ash particles along with main flow is attempted here, to finalize the location of flow correction devices to meet ICAC standard. Uneven distribution of secondary flow happens if the flow is more heterogeneous containing larger coarser ash particles. Large ash particles with significant momentum consistently move towards the nearby located Electrostatic Precipitator (ESP) stream among the all streams in layout, encountering minimal resistance along their path. Typical 800 MW project site reported more heterogeneous flow at ESP inlet, resulting in inefficiency operation as well as frequent shutdown caused by field damage inside ESP chamber. To resolve this, 1:1 scaled computational model was created and two phase numerical simulation was conducted with ANSYS workbench, to revisit the location of existing guide plates at ESP inlet common ducting system. A 3D computational model with appropriate turbulent and other physical parameters was simulated and optimal positioning of guide plates was determined through iterative processes. Engineering capabilities using multi- phase techniques were demonstrated by simulating real-world site conditions, eliminating the necessity for trial-and-error experimentation.
In the two-stage ESP, charging and collection zones are separated, which enhances electrostatic forces and prevents spark discharge but reduces the particle charging time, making the design of the charging zone critical. Besides, existing research usually focuses on the effects of individual parameters on ESP performance, overlooking the interactions between parameters. In this study, we first employ numerical simulations to analyze the particle charging process within the ESP, identifying key design parameters of the charging zone. Then, response surface methodology is utilized to evaluate the influence of different parameters on particle charge levels and energy consumption, aiming to determine the optimal balance. Simulation results show that particles achieve more than 80% of their final charge after passing the first electrode wire, regardless of particle diameter, with a deposition ratio of 10%. While increasing the number of electrode wires can further enhance particle charge, it also increases the chance of back corona occurrence. Response surface analysis indicates that electric field strength has the greatest impact on particle charging, particularly for particles larger than 1 μm. However, as particle diameter decreases and the charging mechanism shifts to diffusion charging, the influence of the charging unit length and the electrode wire radius increases significantly, while the effect of wire-plate distance gradually diminishes, but their interaction remains important. Regarding energy consumption, electric field strength is also the most impactful parameter; as particle charge is increased, energy consumption inevitably rises, yet adjustments in wire-plate distance, which have a lesser effect on particle charging, can reduce energy consumption. The results demonstrate interactive effects among various parameters depending on particle diameter. Thus, design must carefully consider particle diameter effects and the significance of these interactions.
Session 9 “New ESP technique” & “Particle and aerosol charging”
Dielectric Barrier Discharge Type Electrostatic Precipitators – An Overview
The collection efficiency of an electrostatic precipitator (ESP) depends essentially on the migration velocity of the particles toward the collection electrodes. This velocity is at its lowest level for particle sizes between 0.1 and 1 µm. Moreover, a recurring issue with DC discharges in air at atmospheric pressure is the build-up of significant space charges that may result in arc formation. To prevent such events, a straightforward approach consists in inserting a dielectric material between two electrodes. When subjected to an alternative electric excitation, this setup produces a discharge
known as dielectric barrier discharge or DBD.
This paper focuses on the study and development of a dielectric barrier discharge type electrostatic precipitators (DBD-ESP) for the capture of submicron particles. After the presentation of the basic configuration of DBD-ESP, a comparative analysis of the two primary types of DBD-ESP based on their discharge characteristics (filamentary or diffuse) is provided. Subsequently, a discussion on geometrical and electrical optimization is presented to enhance the collection efficiency. The second section of the paper explores the role of electrohydrodynamic flows (EHD) within the DBD-ESP, regarding the charging and collection mechanisms of submicron particles. Specifically, the distinct nature of EHD flows in a DBD-ESP is compared to the one observed in a conventional corona discharge ESP.
Experimental Study on the Electrostatic Removal of Particles from Photovoltaic Panel Surface
Dust accumulation on photovoltaic (PV) panels has become a pressing problem to be solved, as it limits the power generation efficiency and longevity of PV. The conventional methods of particle removal not only consume lots of manpower and water resources, but also the related mechanical equipment is easy to scratch the surface of photovoltaic modules in the inhospitable desert environment. Inspired by the migration and removal of charged particle in electric field within electrostatic precipitators (ESPs), a method of particle electrostatic removal for PV panels self-cleaning was innovatively invented. In this study, an experimental system was designed to explore the dynamic process of particle electrostatic removal. And the role of power supply on particle electrostatic removal was also systematically discussed. The results show that there was a bursting jump phenomenon under the influence of electric field in the dynamic process of particle electrostatic removal. The maximum height of the particle jump observed in this study can exceed 13 mm. Moreover, the maximum particle removal efficiency of 96.10 % was reached at an applied voltage of 3.5kV and a frequency
of 10 Hz within 60 s.
Total Emission Control for Glass Melting Furnace Using Plasma PM Conversion Process
In glass bottle manufacturing plants, products are formed by melting raw materials at ~1500°C using heavy oil and liquefied natural gas (LNG) in a melting furnace. The exhaust gas generated in this process contains nitrogen oxides (NOx), sulfur oxides (SOx), and particulate matter (PM), all of which contaminate the environment when released into the atmosphere. As the conventional exhaust treatment system for the glass melting furnace, a wet or semi-dry desulfurization equipment using sodium hydroxide (NaOH), which reacts easily with sulfur dioxide (SO2), and dust collector such as an electrostatic precipitator and bag filters, which mainly collects are sodium sulfite (Na2SO3) and sodium sulfate (Na2SO4) generated by desulfurization process, are commonly used for desulfurization and PM removal. However, there is no effective NOx removal method because the exhaust gas contains catalyst poison such as sticky dust. A plasma-chemical hybrid process (PCHP) is proposed for simultaneous NOx and SOx treatment. PCHP can be integrated into existing desulfurization reactors by combining plasma oxidation and chemical reduction. In this study, PCHP is applied to an actual glass melting furnace exhaust gas treatment system, achieving simultaneous removal of PM, NOx, and SO2.
Study of Bipolar Pulsed Charge of Submicron Particulate Matter
Electrostatic precipitation technology is an effective method for collecting particulate matter. However, for traditional electrostatic precipitators it is still a challenge to effectively charge and collect fine particles, especially those below one micrometer in size. To address this issue, this article proposes a dual-channel pulsed wire-plate charging structure, coupled with a bipolar pulsed power supply, aimed at improving particle charging efficiency. Experimental results demonstrate that when the peak voltage across a 3 cm discharge gap achieves 26 kV, the particle number concentration decreases by less than 10% following bipolar pulsed charging, and the maximum average charge at the outlet reaches 1800 elementary charges (e). By contrast, DC charging results in a particle number reduction of nearly 90%, with the maximum average charge at the outlet only reaching 500 eC, and the peak voltage at a 3 cm gap being around 21 kV. Under this configuration, pulsed discharge exhibits superior overall charging performance compared to DC charging, and can be used as an effective pre-charging technique for promoting the agglomeration of submicron particles.
The electrification amount and surface potential of liquid droplets falling from a nozzle was measured in order to clarify the charging and discharging properties of droplets formed during automotive spray painting. The electrification amount increased as the applied voltage was increased, peaking at -6 kV before easing off due to the breakup of the droplets and electrical discharging. The ‘electrical surface tension’ was also determined and was nondimensionally correlated with surface charge density. The surface potential for moving droplets, as well as that of stationary metallic disks and spheres, was measured with an electrostatic sensor, and electrostatic sensor principles were applied in an attempt to correct the displayed values according to the size of the droplets. Regression analysis was also used to correct the displayed surface potentials. Discrepancies in electric field values when the sensor part of the electrostatic sensor radially deviated from the central axis of the disk were also investigated.
Charging Phenomena of the High-speed Nanodroplets Impinging on a Copper Plate
Compared with commonly studied microdroplets, nanodroplets have many advanced characteristics (such as being water-saving, non-wettable, having a large surface area, and being chemical agent-free) that can be used for cleaning and sterilization. We proposed a nanodroplet generation methodology using superheated supersonic flow, and the charging effect of the nanodroplets was studied. The electrical current was measured through a copperplate downstream of the flow, and the results suggest that the current value is strongly related to the flow velocity. Supplement to the previous studies, this research also discusses the effect of the temperature of superheated water vapor on the current measurement.
31 October 2024 (Day 4)
Technical Sessions
Session 10 “Applied electrostatics & non-thermal plasma”
Industrial Dielectric Barrier Discharge Plasma for Odor Control
This paper presents one industrial dielectric barrier discharge plasma technique for controlling odor gases emission. The cylinder type home-made ceramic dielectric insulator has outer and inner diameters of 100mm and 80mm, respectively. Its active plasma length is about 800mm. The plasmas are produced on both side of the ceramic tube by applying pulse AC voltage. The main specifications of peak-peak voltage, pulse duration, repetition frequency and average power are around 30-50kV, 25s, 3-5kHz and 50-100kW, respectively. Typical industrial applications are related to food, municipal sewage, incineration power plant, and chemical industries.
IGBT Direct-Drive Nanosecond Pulse Power Supply and Wave Impedance Design of the Reactor
The paper introduces an IGBT direct-drive nanosecond pulse power supply. The output voltage amplitude is 120kV, the output current amplitude is 1000A, the pulse rising/falling edge is about 200ns, the pulse width is 500-2000ns at 50% amplitude, and the repetition frequency is 50-500Hz. It has the characteristics of high efficiency, low failure rate, stability and reliability, utilizing IGBT semiconductor devices and direct output of pulse transformer. In PPCP system, matching the power supply with load-the reactor is crucial. The paper proposes the concept of wave impedance using Uniform Transmission Line model. Through designing the electrode size, insulation and mechanical structure, and series-parallel connection forms of the electrodes, the wave impedance of the reactor is matched with the pulse power supply, and the nanosecond pulse waveform can be transmitted uniformly in the reactor.
Binary hydrocarbons are significant chemical raw material in human life. The large demand for binary hydrocarbons provides new opportunities for the development of advanced technology. The traditional techniques for producing binary hydrocarbons are steam cracking and catalytic cracking. In recent years, the use of discharge plasma assisted reforming of petroleum hydrocarbons to produce light hydrocarbon products has become a promising technology, which mainly includes spark discharge, dielectric barrier discharge, gliding arc discharge and gas phase microwave discharge. In this investigation, binary hydrocarbon was produced by microwave liquid phase discharge technology. At normal temperature condition, plasma is produced by microwave discharge in liquid n-heptane. The reaction is carried out directly in the liquid, simplifying the experimental equipment, reducing energy consumption, and improving the selectivity of binary hydrocarbons. The effects of discharge characteristics and plasma parameters on the generation of binary hydrocarbons were studied. In this work, the energy efficiency of binary hydrocarbons exhibited 3.32 mol/(KW·h), and the selectivity of binary hydrocarbons was 45.9%. Compared with other discharge technologies, microwave discharge technology has significant advantages. This study provides an environmentally friendly and efficient method for the preparation of binary hydrocarbons through n-heptane reforming.
Electrified NOx Formation using Plasma for Power-to-X
Artificial nitrogen fixation using plasma is one of the promising options for electricity-driven valuable compounds which is also referred to as power-to-X (X = H2, NH3, NOx, alcohols, etc) processes. In this work, we present one-step NOx formation by warm plasma, which is characterized by the higher vibrational and rotational temperatures than those of the nonthermal plasmas. High-frequency spark discharge showed much higher performance for NOx synthesis than conventional spark discharge operated at low frequencies. To get insight into the main factors for enhancing energy efficiency and understanding the underlying mechanism, the performance of the reactor was evaluated at different operating conditions. The results revealed that higher vibrational and rotational excitations at a higher frequency and a long electrode gap are critical factors in improving the efficiency of NOx production.
Session 11 “Air purification”
Air Cleaning Performance of a Full-scale Air Handling Unit with a Low-Ozone ESP in a Subway Station
Air handling units (AHUs) are effective in preventing the accumulation of particulate matter (PM) and have the potential to improve air quality. Although AHUs efficiently capture PM on filters, they face energy consumption challenges due to the increased pressure drop associated with PM buildup. An alternative purification system, the electrostatic-type AHU (ES-AHU), leverages electrostatic forces on electrodes to remove PM. When operated with a charging voltage of –20 kV and a collecting voltage of –8 kV, the concentrations of PM2.5 and PM10 were significantly reduced within seconds, achieving removal efficiencies of 99.6% for both. The ES-AHU consistently delivered purified air to the concourse and platform areas. An assessment of the ES-AHU’s impact on individual passengers showed that the removal efficiencies of PM2.5 and PM10 around passengers in the concourse were 63.4% and 63.8%, respectively, while on the platform, they were 61.0% and 59.7%. Thus, the implementation of the ES-AHU not only improves air quality in subway stations but also reduces individual exposure to airborne particulate matter
Study of Fluid-Particle-Fiber Interactions within an Electric Filter Media
Air pollution is a longstanding problem, extending back to the era of the industrial revolution. However, despite its antiquity, it is still a current concern because of its impact on preserving the environment, health and the existence of living species. Electric filter media are widely mentioned in the literature as an effective air purification method. Particle collection using this method operates by various capture mechanisms, influenced by a number of filtration parameters. In this paper, our primary aim is to identify parameters influencing collection efficiency, focusing on the effects of grids voltage and polarity, as well as air flow rate. Results have shown that a reduction in air flow rate and an increase in voltage magnitude enhance the collection efficiency. However, the effect of the voltage polarity is negligible. This study highlights the relationship between these filtration parameters and collection efficiency, providing essential insights to understand electrical capture mechanisms.
Dolachar as Fuel for Boilers and its Impact on ESP
Dolochar is a byproduct of the sponge iron manufacturing process, which involves the reduction of iron ore using non-coking coal. Dolochar is a low-grade fuel that contains high levels of ash, sulphur, and volatile matter. It is typically used as a fuel in small sponge iron power plants like Atmospheric fluidized bed combustion boiler (AFBC) and circulating fluidized bed combustion boiler (CFBC) with coal at a mixture of 70 %-30 % maximum, but its use is limited due to its low calorific value and high ash content. However, this fuel is currently trending in India due to its availability and it’s commercial feasibility. Electrostatic precipitators (ESP’s) struggle to perform with Dolochar as fuel; these particles re-entrain easily because of its low resistivity. High carbon ash can also cause increased sparking and reduce secondary voltage levels in the ESP resulting in the rejection of corona power by ESP.
In this paper we are presenting the limitations, and advantages of Dolochar as a fuel and how AFBC boiler customers have tried different electrical energization solutions in their ESP’s like using 3 Phase technology or having installed 20 KHz power supplies to reduce the emission to the designed or less than the designed emission but have finally got the result after installing Ador REDKOH IGBT based Power Supplies resulting in emission reduction to the desired 30 mg/nm3 from 120 mg/nm3 without any shut down of ESP or change in the percentage of Dolochar with Coal.
Fog Dispersion using High Voltage Charged Particles
At many airports specifically during cold and moist weather, fogging condition is formed resulting to low contrast and poor visibility, either early morning, late evening or for the entire day during winters. The fog retention period depends upon many climatic conditions which cannot be predicted accurately.
There is adverse effect of fog on Air traffic resulting in flight delay, and sometimes cancellation of flights. This delay and cancellation of flight causes inconvenience to the passengers apart from huge commercial losses to airlines. This paper describes an experimental experience on the usage of charged particle flow to precipitate the fog and increase the visibility. This is an applied research based on the operational principle of Electrostatic Precipitators.
Session 12 Environmental improvement technology” & “Plasma fundamental & diagnostics”
Generation of Thermal Plasma for Chemical Conversion Process
A study on the CH₄ direct conversion using a thermal arc plasma has been conducted. In the study, both CH₄ direct conversion and generation of gliding arc have been investigated. The CH₄ direct conversion experiment demonstrated that adding hydrogen (H₂) to the argon (Ar) carrier gas of the arc plasma torch has beneficial effects, such as suppressing carbon formation and reducing the energy cost required for C₂H₂ production. Since the characteristics of arc generation for the CH₄ direct conversion process change significantly with addition of H₂, a detailed investigation on gliding arc plasma with H2 addition has been also conducted. The gliding arc experiment, in which a gliding arc is generated at various H₂ concentrations, showed that rapid transfer of thermal energy from the H2 in the arc column to the surrounding gas plays a key role in determining the arc generation and extinction characteristics.
Reduction of Carbon Dioxide Particles to Carbon Monoxide by Nonthermal Plasma
Nonthermal plasma reduces carbon dioxide to carbon monoxide, which can be converted to fuels, organic compounds, and used as a raw material for gas synthesis. However, this energy efficiency is currently low for practical use, and innovative ideas are needed. This study proposes a CO2 fuel conversion technology using solid CO2 in a nonthermal plasma reactor. The advantages of using solid CO2 are expected to be suppression of CO re-oxidation reaction at low temperatures and improvement of energy efficiency by high concentration of CO2. In the experiment, plasma reduction of gas and solid CO2 is performed using a dielectric barrier discharge plasma reactor, and the conversion and energy efficiency are compared. As a result, it is found that the generated CO concentration is dependent on the concentration of CO2. When nonthermal plasma is applied to solid CO2, the Joule heating causes the CO2 to sublimate, which reduces the gaseous CO2 to CO. Solid CO2 in the plasma reactor increases the impedance and decreases the discharge power. By introducing solid CO2 upstream of the reactor, the discharge power increases, and the conversion efficiency to CO improves. At a specific energy of 1.8 eV/molecule, the reduction of solid CO2 increases conversion efficiency from 1.4% to 1.8% and energy efficiency from 2.3% to 2.7% compared to the reduction of gaseous CO2.
Effects of Mixture Gas of Ar and He on Plasma-driven Liquid Flows
Plasma-driven liquid flows that are generated in bulk liquid by plasma irradiation are one of the key factors in understanding the interaction between plasma and liquid. In this work, plasma-driven liquid flows were investigated using particle image velocimetry when the supplied gas composition (He [%] / Ar [%]) for plasma generation were changed. The effects of the supplied gas composition on the plasma-driven liquid flows depended on frequency. At 4 kHz and below, the supplied gas composition affected only the speed of the liquid flows in the same direction. On the other hand, at 7 kHz and above, the supplied gas composition affected not only the speed but also the direction of the liquid flows.
Session 13 “Particle and aerosol charging” & “ESP operation and maintenance”
Household-scale electrostatic precipitators can help reduce particulate matter concentrations in cities and industrial sites. As there has been little demand for such developments over the decades, most of the literature is on laboratory pilot projects with some practical experience.
We built a small-scale electrostatic precipitator complemented by a dust dispenser during our research. We attribute the efficiency of the particle collection mainly to differences in mass measurements, but we also performed field strength measurements in parallel. In our investigations, we constructed the dust collection tray from a conductive material so we could calculate the accumulated potential as a function of time and, thus, the total charge. From our results, we can clearly see the static charge accumulation in the conductive tray via the corona electrodes and the added amount of dust charge by dust particles.
Electrostatics of Granules and Granular Flows
In past decades, the electrostatics of granules and granular flows has obtained more and more attention due to many industrial problems and the associated development of new technologies. Granule-wall collision causes electrification, where charge transfer can be characterized by work function, electron transfer, ion transfer, and material transfer. Electrification is affected by many factors and increases with granule processing, and the charge amount can reach a saturated state where electrification no longer increases, which has been confirmed by single granule and granule conveying systems. In addition, the presence of electrostatic charges has profound influences in relevant areas, including chemistry, chemical engineering, energy, pharmaceuticals, and so on. The measurement technology of electrostatics used in granule conveying systems has been improved with the continuous progress of industry. Furthermore, electrostatics of granules and granular flows will be developed into a more accurate area together with other subjects as an interdisciplinary problem to be concerned. In addition, in the pneumatic conveying system, granule-wall and granule-granule collision or friction can cause material transfer due to material breakage. The working mechanism of the material transfer due to collision or friction has never been fully understood. Such problems will be solved gradually in the future.
High voltage power supplies are an integral and important part of optimal running of Electrostatic Precipitator (ESP). Still. Any issues in these high voltage power supplies, will affect the performance of the ESP. It is utmost necessary to keep the ESP power supplies healthy all the time. This paper talks about our experience at various installations in India, and how this has helped customer, on prognosis of the High Voltage Power supply health, and eliminate the potential failures or potential issues by remotely monitoring, acquiring, and analyzing the data using Internet of Things (IoT). The
trademark name of our system is “Max Smart” This has helped the customers to keep the ESP Uptime high and with the help of Artificial Intelligence (AI) we are heading towards prediction of any failure even before it occurs. In this paper we are presenting how to implement AI for prognosis of HV rectifiers and control cabinet to help customers to have an early intimation of any potential issue and thus to implement predictive maintenance in advance to eliminate or minimize the electrical shutdown.
ESP Troubleshooting with Machine Learning Analysis
Several industries are working to harness the power of Artificial Intelligence (AI) to improve safety, quality control, increase productivity, performance, efficiency, and customer satisfaction. AI is transforming businesses in a similar way to how electricity transformed industries over 100 years ago. Random Forests (RF) are classified as Ensemble Machine Learning-Supervised algorithms that can be applied to solve classification or regression type problems. RFs utilize decision trees which are simplified algorithms where significant research has been abundantly conducted in terms of measuring variable importance. In a recent EPRI project, the analytical capability of the regression RF and a novel Forest of Forests algorithm have been integrated into a desktop application called Forest Ensemble Machine Learning (ForEMaL) Explorer. The FoREMaL Explorer prototype was utilized to analyze a known performance issue of the particulate matter control system, a cold-side electrostatic precipitator, at a 640 MWg coal-fired electrical generating unit (EGU.) To construct the RF model, 300 process DCS tags (features) were selected and included: Unit gross load, TR-Set voltages, TR-set currents, spark rates, firing angles, IDF motor current, IDF control vane positions and opacity. This paper provides a summary overview of the approach, machine learning analysis, and its potential utilization across other processes.
Session 14 “Bacteria elimination/inactivation/bio & organism-related technologies”
A New Plasma Technology Used for Cold-chain Disinfection (Invited)
Cold-chain transport is an important way for cross-regional transmission of pathogenic microorganisms, so an efficient sterilization technology is urgently needed for cold-chain environment. Cold atmospheric plasma (CAP) has demonstrated excellent sterilization capabilities in biomedical applications. In particular, it is found to be effective for the inactivation of pseudoviruses with the SARS-CoV-2S protein in cold-chain environments. Therefore, CAP has substantial potential to be developed as a new technology for cold-chain sterilization, but further studies are needed to validate its effectiveness in cold-chain environments as well as to enhance its efficiency to meet practical application requirements. In view of this, a novel plasma technology by the combination of NOx mode and O3 mode air discharges (mode-combination method), is proposed for sterilization in cold-chain environment. The mixed gas produced by mode-combination method can effectively inactivate bacteria in ice at different temperatures, which is a significantly stronger effect than that of either the NOx-gas or the O3-gas alone. Moreover, compared to that of O3-gas, the inactivation effect of the mixed gas can penetrate deep into the ice layer, which is associated with the penetration of reactive species. This strong inactivation effect is primarily attributed to the high-valence nitrogen oxides (NO3 and N2O5) rich in the mixed gas. Our findings provide a promising sterilization strategy to curb the spread of infectious diseases in cold-chain environments.
Microbial Inactivation of Whole Black Pepper using Dielectric Barrier Discharge
Black pepper, after harvesting, is dried to become a product, but its manufacturing process lacks microbial control and contains many heat-resistant spores. Currently, microbial inactivation of whole black pepper is carried out using superheated steam, however, which results in the loss of the rich aroma inherent in black pepper. As an alternative microbial inactivation method that preserves the aroma of pepper, we focused on the dielectric barrier discharge (DBD) for microbial inactivation. Multiple electrodes covered with quartz glass tubes were arranged and connected to a ground and a high-voltage power supply, and DBD was generated between these electrodes by applying high alternating-current voltage (9.5 kV, 20 kHz) to them. Microbial inactivation was conducted by exposing the whole black pepper to this discharge plasma. Air was blown from under the arranged electrodes for agitating and cooling the whole black pepper. By investigating the continuous contact time with DBD, total treatment time, and humidity conditions of the atmosphere and the whole black pepper, inactivation of heat-resistant spores in whole black pepper by about 3 log10 was achieved. Furthermore, analysis of the aroma compounds of the treated whole black pepper (α-Pinene, β-Pinene, β-caryophyllene, and limonene) showed that the DBD treatment had small impact on these compounds
In order to achieve high collection efficiencies for nano-sized particles and airborne viruses with low ozone generation, the effect of the number of carbon brushes was investigated in an electrostatic precipitator with a carbon brush disk electrode in this study. The ESP was a two-stage type consisting of a precharger and a collector. The precharger was composed of a coaxial cylindrical structure consisting of a carbon brush disk electrode and a grounded cylindrical electrode. Carbon brushes were arranged around the circumference of the disk electrode in numbers ranging from 5 to 20, or continuously. The collector was a parallel plate configuration. A positive DC high voltage between 10 and 20 kV was applied to the precharger to maintain an ozone concentration between 0.01 and 0.03 ppm, while a positive DC voltage of 9 kV was applied in the collector. The gas velocity inside the duct was adjusted to 0.3 or 0.6 m/s. The collection efficiencies for nano to micro-order sized particles and airborne viruses were measured. As a result, a high collection efficiency of 80% to greater than 90% was achieved with the low ozone concentration of 0.01 ppm. Furthermore, the collection efficiency improved as the number of brushes increased. By arranging the brushes continuously, a collection efficiency of greater than 99% was achieved for particles larger than approximately 34 nm. Additionally, a collection efficiency greater than 97% for airborne viruses was achieved at an ozone concentration lower than 0.03 ppm.
Session 15 “Plasma fundamental & diagnostics” & “Applied electrostatics & non-thermal plasma”
Application of Optical Wave Microphone CT Scan to Corona Discharge
An optical wave microphone has potential applications in various kinds of acoustic waves. It was successfully built utilizing Fraunhofer diffraction of a laser beam to detect pressure waves. Recently, the fibered optical wave microphone developed and it has an improved signal-to-noise ratio compared with that of a conventional optical wave microphone. The fibered optical wave microphone is basically composed of a probe laser beam, lens and photo detector. The diffracted laser beam passes a lens and optical Fourier transform can be done at the focal point of the lens where the detector locates. The fibered optical wave microphone has superior sensitivity compared to the other optical techniques because it works based on Fraunhofer diffraction between the probe laser and the refractive index change of acoustic waves. This technique is able to be combined with computer tomography (CT) and the authors previously succeeded to detect shockwaves generated from micro-plasmas and visualize two-dimensional distribution of acoustic emission from non-thermal plasmas such as dielectric surface barrier discharge. In this work, fundamentals about quantification of sound pressure using theoretical model of optical wave microphone is introduced. Then, acoustic emission from corona discharge (BJS300, Shishido) operated by a power supply (SAT-11 ELIMINOSTAT, 60 Hz, 7 kV) was examined with this technique and two-dimensional distribution of acoustic emission above the corona discharge device was visualized by the optical wave microphone CT scan.
Non-oxidative Microwave Plasma Reforming of Plastic
The increasing amount of plastic waste every year leads to discussions on the proper management of the material. Despite recycling being regarded as a favorable treatment method for plastic waste, its mechanical property is degraded after several recycling procedures. In fact, most plastic waste is littered or landfilled; 60% of the globally generated plastic waste from 1950 to 2015 was dumped. Otherwise, plastic waste can be permanently disposed of by thermochemical treatments such as incineration, pyrolysis, and gasification process with a chance of energy recovery. Whereas, CO2 emission from the thermochemical treatments is substantial, even comparable to those from fossil fuel powerplants. The CO2 mostly emanates from the carbon content of plastic waste and is emitted directly to the atmosphere or captured at the implanted carbon capture and storage (CCS) system. Alternatively, this study suggests converting the carbon content to solid carbon and recovering the energy of plastic waste using microwave plasma under a non-oxidative high- temperature environment. An experiment was conducted by feeding plastic powder to Argon plasma gas. This system captured solid carbon and H2, CH4, C2H2, C2H4 species were produced. To enable stable operation of the reactor, removal of the captured solid carbon in the reactor would be further investigated in the future work.
The EHD Flow Field in the CRSS using the AI Image Analysis
A method using atmospheric pressure non-thermal equilibrium plasma is known as one method for treating gases such as NOx and SOx discharged from thermal power plants and factories. One of the methods for treating exhaust gases such as NOx is a method using a Corona Radical Shower System (CRSS), and the electrohydrodynamic flow field in an atmospheric pressure non-thermal equilibrium plasma has been analyzed using the Schlieren method. The Schlieren method can visualize heterogeneous states of transparent gases, liquids, and solids as density gradients, which are difficult to see with the naked eye. This is a method in which parallel light is transmitted through an object and observed as a difference in brightness and darkness due to slight changes in the refractive index due to density gradients.
Figure 1 shows a schematic diagram of image processing for the electrohydrodynamic flow field in a corona radical shower system using AI image analysis. The Schlieren images of the EHD flow field in CRSS are the images taken when I received my degree from the doctoral course at Oita University in 2006.
In this study, I created an AI image analysis tool and reported that I obtained indicators for the analysis of electrohydrodynamic flow fields in CRSS using the Schlieren method.
