T. Czech

Back-corona generated plasma for decomposition of hydrocarbon gaseous contaminants

A back-corona discharge has been tested as a plasma source for decomposition of hydrocarbons . A back-corona discharge has hitherto not been applied for these purposes. The results of laboratory experiments show that the back-corona discharge can decomposite hydrocarbons, similarly to a dc or pulsed streamer corona discharge, with similar energy expense and conversion rate. However, the final concentration of after the same residence time of 60 s is lower for back-corona discharges. The back-corona also produces less CO and during the decomposition process.

Dust particles motion in back discharge

The back discharge is a type of discharge that takes place in the electrostatics precipitation process, especially in coal-fired power plants for coal of low content of sulfur. This type of discharge takes place in the presence of corona discharge and occurs on an electrode covered with a high resistivity dust layer. The breakdown of dielectric layer causes an increase in the discharge current and re-entrainment of dust particle from collection electrode into the flowing gas. The investigations of the motion of dust particle emitted from the collection electrode are presented in this paper. Additionally, acrylic powder layer placed between a mica plate with a small pinhole and the plate electrode were also used in the experiments in order to generate repeatable back discharge. An effect of back discharge on the collection efficiency in the electrodes system was also presented.

Removal of NOx from NO2∶NO∶N2 mixture by a pulsed and dc streamer corona in a needle-to-plate reactor

The results of laboratory experiments on reduction of NOx in the oxygen free gas mixture NO2∶NO∶N2 simulating exhaust gas, by means of pulsed and dc streamer corona discharges generated in a needle-to-plate reactor have been presented. The results show that the dc corona discharge is more efficient in De-NOx process than the pulsed corona discharge. This is in contrast to the results obtained in the wire-to-cylinder reactors where the pulsed corona discharge removes NOx more efficiently. The results also lead to the conclusion that in the dc streamer corona discharge the short pulses and long interelectrode distances are recommended in order to increase the NOx conversion rate.

Dust particles precipitation in AC/DC electrostatic precipitator

Submicron and nanoparticles removal from flue or exhaust gases remain still a challenge for engineers. The most effective device used for gas cleaning in power plants or industry is electrostatic precipitator, but its collection efficiency steeply decreases for particles smaller than 1 micron. In this paper, fractional collection efficiency of two-stage electrostatic precipitator comprising of alternating electric field charger and DC supplied parallel-plate collection stage has been investigated. The total number collection efficiency for PM2.5 particles was higher than 95% and mass collection efficiency >99%. Fractional collection efficiency for particles between 300 nm and 1 μm was >95%.

Electrostatic method for the production of polymer nanofibers blended with metal-oxide nanoparticles

The paper presents investigations of a method of the production of non-woven polymer fabrics with incorporated metal oxide nanoparticles based on electrospinning and electrospraying. Two main configurations of electrospraying/electrospinning systems have been tested: two-step process of electrospinning of polymer solution followed by electrospraying of nanoparticle suspension, and simultaneous electrospinning of polymer solution and electrospraying of nanoparticle suspension. By this method TiO2, MgO, or Al2O3 nanoparticles of the size from 20 to 100 nm were deposited onto electrospun PVC nanofibers.

Spectroscopic studies of back-discharge

Different forms of low current back-discharge in air at atmospheric pressure with fly ash used as a dielectric barrier are discussed in the paper. The discharge was characterized in terms of optical emission spectra and current-voltage characteristics. The discharge emission spectra in the wavelength range of 200÷540 nm have been measured to investigate behavior of the species present in the fly ash when back-discharge is initiated. In normal conditions the emission spectra are dominated by atmospheric components (molecular nitrogen, atomic oxygen and nitrogen) but atomic lines due to chemical composition of the fly ash were also identified.

SUBMICRON PARTICLES EMISSION CONTROL BY ELECTROSTATIC AGGLOMERATION

An alternating electric field charger/agglomerator, in which particle charging and their coagulation occurs in one stage, is presented in this paper. Th e charger/agglomerator is based on an alternating e lectric field charger formed by a set of two discharge electrodes separated by a set of two parallel grids by each s ide of the discharge electrodes. The particles are charged by ionic current in alternating electric field that al lows the charge imparted to the particles to be higher than for DC chargers. Due to oscillatory motion of the particle s between the electrodes, particles of different mobilities c an collide and coagulate. Number fractional collect ion efficiency of PM2.5 particles in semi-industrial scale, two-st age charger/agglomerator with precipitator section was higher than 90%.

Studies of Low‐Current Back‐Discharge in Point‐Plane Geometry with Dielectric Layer

The paper presents results of spectroscopic investigations of back‐discharges generated in the point‐plane electrode geometry in ambient air at atmospheric pressure, with the plane electrode covered with a dielectric layer. Fly ash from an electrostatic precipitator of a coal‐fired power plant was used as the dielectric layer in these investigations. The discharges for positive and negative polarities of the needle electrode were studied by measuring optical emission spectra at two regions of the discharge: near the needle electrode and dielectric layer surface. The visual forms of the discharge were recorded and correlated with the current‐voltage characteristics and optical emission spectra. The back‐arc discharge was of particular interest in these studies due to its detrimental effects it causes in electrostatic precipitators.

The influence of NH3 on NO2 conversion in a dc corona discharge in N2:O2:CO2:NO2:NH3 mixture

The aim of this paper is to investigate the influence of NH3 additive (540–1470 ppm) on the conversion of NO2 and the creation of NO and N2O in a mixture of N2:O2:CO2: NO2:NH3 subjected to the so-called direct current (dc) corona discharge. The dc corona discharge was generated in a needle-to-plate reactor. Seven positively polarized needles were used as one electrode and a stainless steel plate as the other. The time-averaged discharge current was varied from 0 to 7 mA. It was found that the dc corona discharge decomposed NO2 and produced NO and N2O. The reduction of NO2 was higher without NH3 additive if the residence time of the operating gas was relatively short. However, in a longer corona discharge processing the NH3 additive may be useful for reduction of NO2.