Panich Intra

Design and Evaluation of a High Concentration, High Penetration Unipolar Corona Ionizer for Electrostatic Discharge and Aerosol Charging

The aim of this paper is to design and evaluate a high concentration, high penetration unipolar corona ionizer. The electrostatic characteristics in terms of voltage-current relationships of the present ionizer in the discharge zones for positive and negative coronas were discussed. Using ion current measurement, the concentration and penetration of ions were evaluated at corona voltages across the needle electrodes between 1 and 4 kV, flow rates between 1 and 5 L/min, and an operating pressure of 1 atm. In the discharge zone of the ionizer, the highest ion concentrations were found to be about 1.71×10 14 and 5.09×10 14 ions/m³ for positive and negative coronas, respectively. At the outlet of the ionizer, it was found that the highest ion concentration was about 1.95×10 13 and 1.91×10 13 ions/m³ for positive and negative coronas, respectively. The highest ion penetration for positive and negative coronas through the ionizer was found to be about 98 % and 33 %, respectively. The Nit product for positive and negative coronas was also found to 1.28×10 13 and 7.43×10 13 ions/m³s, respectively. From the findings, this ionizer proved to be particularly useful as an aerosol charger for positive and negative charge before the detector in an electrical aerosol detector.

Particulate Emission Reduction from Biomass Burning in Small Combustion Systems with a Multiple Tubular Electrostatic Precipitator

Biomass utilization via combustion is gaining an increasingly important role worldwide in heat and power production. Emissions of particulate matter from biomass burning have drawn considerable attention because of concern over their possible toxicity and implications for human health. For small-scale applications, it is desirable to employ a simple, compact, and inexpensive solution to avoid air quality problems related to biomass combustion. Electrostatic precipitation is a very reliable method to control particulate emissions from boilers, incinerators, and other industrial processes. It is therefore applied to small combustors. In this work, a simple, compact, and cost-effective multiple tubular electrostatic precipitator was designed and evaluated theoretically and experimentally for removal of particulate matter from a small biomass combustor. The precipitator consisted of a simple array of coaxial discharge electrodes placed along the axis of each cylindrical collection tube. The discharge electrodes were connected to the positive high-voltage supply, while the cylindrical collection tubes were grounded. The positive high-voltage supply was used to produce the corona discharge field between individual discharge electrode and collection tube. The particle-laden exhaust gas flow from the small biomass furnace was directed across the corona discharge field and then charged. The charged particles were deflected outward in a radial direction and deposited on the collection tube wall. The overall collection efficiency of the electrostatic device was evaluated as a mass loading ratio of the difference at inlet and outlet to the particle loading at the inlet of the device. It was found that about 70% overall collection efficiency can be achieved with a relatively simple multiple tubular electrostatic precipitator design. The device appeared to be a promising tool for reduction of particulate matter in flue gas from a small biomass combustion system.

Development of a PM 2.5 sampler with inertial impaction for sampling airborne particulate matter

A simple and low cost PM2.5 impactor for sampling airborne particulate matter was developed, designed and evaluated. The design was an assembly of an acceleration nozzle and an impaction plate. Particles with sufficient inertia were unable to follow air streamlines and impacted on the plate. Smaller particles followed the streamlines, avoided being captured by the plate and could then be collected on a downstream filter. Analytical and numerical models were formulated to predict collection efficiency, flow fields and vectors, and particle trajectories in the impactor. The modeling suggested that an optimal operational domain exists for the PM2.5 impactor. A prototype was then built and tested. The collected particles on the impaction plate and downstream of the PM2.5 impactor were analyzed by using scanning electron microscopy. Experimental results agreed well with the theoretical predictions. Testing of the PM2.5 impactor prototype showed promising results for this airborne particulate matter sampler.

Comparative Study on Electrical Discharge and Operational Characteristics of Needle and Wire-Cylinder Corona Chargers

The electrical discharge and operational characteristics of needle and wire-cylinder corona charger based on current measurements for positive and negative coronas were evaluated and compared. A semi-empirical method was used to determine the ion concentrations in the charging zone and at the outlet of both chargers. Results from experimental investigation revealed that magnitudes of the charging current from the wire-cylinder charger were approximately 3.5 and 2 times smaller than those from the needle charger for the positive and negative coronas, respectively. The ion number concentrations at the outlet for positive corona of both chargers were higher than for negative corona at the same voltage. Flow and electric fields in the charging zone of both chargers were also analyzed via numerical computation. Strong electric field strength zone was identified and led to high charging and particle deposition. Effect of particle deposition on the evolution of discharge current was presented. It was shown that ions loss inside the wire-cylinder charger was higher than the needle charger. The particle deposited on the corona electrodes and on the grounded cylinder caused a great reduction in charging efficiency of both chargers.

Demonstration of a Modular Electrostatic Precipitator to Control Particulate Emissions from a Small Municipal Waste Incinerator

Incineration is conceptually sound as a waste treatment technology. There is, however, concern over its emissions when it is improperly designed and operated. An electrostatic precipitator is one of the most commonly used devices to control particulate emissions from boilers, incinerators and some other industrial processes. In this work, a modular electrostatic precipitator with sizing of 1 m × 1 m×1 m was developed for removal of particulate matter from the exhaust gases of a small waste incinerator. Its design was based on a simple wire-and-plate concept. The corona discharge wires were connected to a positive high-voltage pulse generator, while the collection plates were grounded. The high-voltage pulse generator was used to produce the corona discharge field between the individual discharge wire and the collection plate. The particulate-laden exhaust gas flow was directed across the corona discharge field. The charged particles were deflected outward and collected on the plate. The collection efficiency was evaluated as a mass loading ratio between the difference at the inlet and the outlet to the particulate loading at the inlet of the precipitator. The collection efficiency of this modular electrostatic precipitator design was approximately 80 %.

An electrostatic sensor for the continuous monitoring of particulate air pollution

We developed and evaluated a particulate air pollution sensor for continuous monitoring of size resolved particle number, based on unipolar corona charging and electrostatic detection of charged aerosol particles. The sensor was evaluated experimentally using combustion aerosol with particle sizes in the range between approximately 50 nm and several microns, and particle number concentrations larger than 1010 particles/m3. Test results were very promising. It was demonstrated that the sensor can be used in detecting particle number concentrations in the range of about 2.02×1011 and 1.03×1012 particles/m3 with a response of approximately 100 ms. Good agreement was found between the developed sensor and a commercially available laser particle counter in measuring ambient PM along a roadside with heavy traffic for about 2 h. The developed sensor proved particularly useful for measuring and detecting particulate air pollution, for number concentration of particles in the range of 108 to 1012 particles/m3.

Development and Evaluation of a Faraday Cup Electrometer for Measuring and Sampling Atmospheric Ions and Charged Aerosols

A simple and inexpensive Faraday cup electrometer for measuring and sampling ion and aerosol charge was developed and evaluated. It consists of a Faraday housing, a filter holder, a high efficiency particulate air (HEPA) filter, Teflon® insulator, and electrometer housing. In the Faraday cup, the ion and aerosol charge entered the electrometer and then collected on the filter. All ion and aerosol charges were induced and generated an ultra-low current of less than 10 pA corresponding to the number concentration of ion and aerosol. The performance of the prototype electrometer circuit was calibrated with a current injection circuit, high-impedance current source and compared with theoretically and numerically predictions. Good agreement was found from the comparison. Experimental testing of ion and aerosol charge measurements were carried out for different operating air-flow rates for both positive and negative ions. Ion and aerosol charge measurements were also performed. Finally, this Faraday cup electrometer proved particularly useful as an ion and aerosol charge sampler and detector for both positive and negative ions.

Investigation on the electrical discharge characteristics of a unipolar corona-wire aerosol charger

In the present study, a simple corona-wire charger for unipolar diffusion charging of aerosol particles is designed, constructed, and characterized. Experimental characterizations of the electrostatic discharge in terms of current-voltage relationships of positive and negative coronas of the corona-wire charger are also presented and discussed. The charging current and ion concentration in the charging zone increased monotonically with corona voltage. The negative corona showed higher current than the positive corona. At the same corona voltages, the current in the discharge zone is about 600 times larger than the charging current. The ion number concentrations ranged within approximately 5.0 × 10 10 to 1.24 × 10 16 and 4.5 × 10 12 to 2 × 10 16 ions/m 3 in the discharge and charging zones, respectively. A numerical model is used to predict the behavior of the electric potential lines. Numerical results of ion penetration through the inner electrode are in good agreement with the experimental results.

Comparison of electrostatic charge and beta attenuation mass monitors for continuous airborne PM10 monitoring under field conditions

An electrostatic PM10 mass monitor (EPMM) used for wireless continuous airborne particulate matter monitoring was developed and evaluated in our previous work. However, differences in measured PM10 mass concentrations between the electrostatic charge and the beta ray attenuation methods due to the frequent occurrence of high humidity and temperature in the ambient air in Thailand’s have not been extensively studied in our previous work; and in the literature, it would be necessary to compare the output of the EPMM against the beta ray attenuation mass monitor. In this study, we evaluated the performance of the EPMM simultaneously with a commercially available FH62C14 Beta gauge continuous ambient particulate monitor, Thermo Fisher Scientific Inc., for PM10 measurements at ambient condition in the field. The measurements were made at Yupparaj Wittayalai School, Si Phum, Mueang, Chiang Mai, Thailand from November 16-23, 2015. They showed that the averages of PM10 mass concentrations measured by the EPMM linearly correlate very well with the PM10 mass concentrations measured by the FH62C14. The slopes were 0.9620 and 1.0649 for 1 and 24-hour, respectively, and R2 of 0.8634 and 0.9889 for 1 and 24-hour, respectively. Finally, this comparison proved to be particularly useful in the refinement and design of the EPMM.

Electrostatic Evaluation of a Unipolar Diffusion and Field Charger of Aerosol Particles by a Corona Discharge

This article presents a unipolar diffusion and field charger by corona discharge is presented and electrostatically evaluated for charging aerosol particles. The electrostatic characteristics of the charger were investigated with an electrometer by measuring the ion number concentrations corresponding to the discharge and charging currents. The discharge and charging currents, and ion number concentration in the discharge and charging zones of the charger, increased with corona voltage. The magnitudes of the ion number concentration for positive and negative coronas in the discharge zone ranged from 1.34 × 1013 to 1.84 × 1015 ions/m3 and 7.34 × 1013 to 2.64 × 1015 ions/m3, respectively. For the charging zone, the ion number concentrations for positive and negative coronas ranged from 2.95 × 1013 to 1.52 × 1014 ions/m3 and 2.06 × 1013 to 1.47 × 1014 ions/m3, respectively. To predict the behavior of the electric field strength and lines in the discharge and charging zones of the charger, the electric field strength and distribution of the charger in the discharge and charging zones were calculated by a commercial computational fluid dynamics software package. Numerical calculation results of electric field distribution and lines through the inner electrode showed good agreement with experimental results. Also, the mean charge per particle for particle diameters were in the range of 0.01 to 50 µm for various operating conditions of the charger was theoretically evaluated. For both diffusion and field charging, lower aerosol flow rate and higher corona voltage resulted in an increase in the mean charge per particle within the charger. This simple charger proved to be particularly useful in diffusion and field charging of aerosol particles in particulate matter detector instruments for measuring PM10 and PM2.5 concentration.