Milorad M. Kuraica

A dual-use of DBD plasma for simultaneous NOx and SO2 removal from coal-combustion flue gas

Dielectric barrier discharge (DBD) was investigated for the simultaneous removal of NO(x) and SO(2) from flue gas in a coal-combustion power plant. The DBD equipment was used in either a mode where flue gas was directed through the discharge zone (direct oxidation), or a mode where produced ozonized air was injected in the flue gas stream (indirect oxidation). Removal efficiencies of SO(2) and NO for both methods were measured and compared. Oxidation of NO is more efficient in the indirect oxidation, while oxidation of SO(2) is more efficient in the direct oxidation. Addition of NH(3), has lead to efficient removal of SO(2), due to thermal reaction, and has also enhanced NO removal due to heterogeneous reactions on the surface of ammonium salt aerosols. In the direct oxidation, concentration of CO increased significantly, while it maintained its level in the indirect oxidation.

Decolorization of reactive textile dyes using water falling film dielectric barrier discharge

Decolorization of reactive textile dyes Reactive Black 5, Reactive Blue 52, Reactive Yellow 125 and Reactive Green 15 was studied using advanced oxidation processes (AOPs) in a non-thermal plasma reactor, based on coaxial water falling film dielectric barrier discharge (DBD). Used initial dye concentrations in the solution were 40.0 and 80.0mg/L. The effects of different initial pH of dye solutions, and addition of homogeneous catalysts (H(2)O(2), Fe(2+) and Cu(2+)) on the decolorization during subsequent recirculation of dye solution through the DBD reactor, i.e. applied energy density (45-315kJ/L) were studied. Influence of residence time was investigated over a period of 24h. Change of pH values and effect of pH adjustments of dye solution after each recirculation on the decolorization was also tested. It was found that the initial pH of dye solutions and pH adjustments of dye solution after each recirculation did not influence the decolorization. The most effective decolorization of 97% was obtained with addition of 10mM H(2)O(2) in a system of 80.0mg/L Reactive Black 5 with applied energy density of 45kJ/L, after residence time of 24h from plasma treatment. Toxicity was evaluated using the brine shrimp Artemia salina as a test organism.

Plasma diagnostics of the Grimm-type glow discharge

Abstract Results of argon-hydrogen plasma diagnostics in the plane cathode Grimm-type glow discharge are presented. Radial distributions of electron excitation temperatures, electron density and temperature of excited hydrogen atoms are reported. A numerical procedure necessary for the evaluation of the electron density and the temperature of excited hydrogen atoms from the profiles of hydrogen Balmer lines has been developed. The algorithm can be applied to the sum of an arbitrary line profile if they are convolved with a Gaussian profile.

Spectroscopic measurement of electric field in atmospheric-pressure plasma jet operating in bullet mode

Atmospheric-pressure helium plasma jet operating in the bullet/streamer mode has been studied using optical emission spectroscopy. Electric field strength distribution is measured using Stark polarization spectroscopy of He I 492.19 nm line. It is shown that the electric field is almost constant along the jet axis. Measured electric field distribution is in agreement with theoretical predictions of streamer propagation in helium jets at atmospheric pressure. Obtained radial distribution of the axial electric field shows that the ring-shaped structure of the light emission is a consequence of such electric field distribution.

Spatio-temporally resolved electric field measurements in helium plasma jet

The focus of this paper is on the spatially and temporally resolved measurements of the electric field in atmospheric-pressure plasma jets operating in helium. Using the Stark polarization spectroscopy method, temporal development of the electric field was observed in steps which were in range of 20–500 ns. Such temporal resolution was complemented by the spatial resolution of 0.025 mm. Depending on the plasma jet configuration, the maximal electric field strength in the bullet/streamer head was between 10 and 20 kV cm−1. Electric field measurements are accompanied by the electrical and spectroscopic diagnostics of the discharge evolution. It was found that without the grounded electrode downstream from the nozzle, the jet develops as the cathode directed streamer. Contrarily, when a grounded electrode is present, development of the plasma jet is very similar to the evolution of the single microdischarge in air. Finally, the direct relation between electric field strength and the velocity of the plasma bullet is demonstrated.

Excessive Balmer line broadening in a plane cathode abnormal glow discharge in hydrogen

Results of a Doppler spectroscopy study of the hydrogen Balmer alpha line in an abnormal glow discharge operated in pure hydrogen are reported. Measurements of line shapes are performed side-on to the discharge axis in a low electric field region of negative glow. The excessive Balmer alpha broadening is detected and its presence and linewidth is related to the collisions of fast hydrogen atoms with molecular hydrogen. The collision model enabled also an estimation of effective cross section data from the Balmer alpha axial intensity decay curves. Large excessive Balmer alpha line broadening in pure hydrogen and its dependence upon the direction of observation with respect to the electric field is in contradiction to the resonance transfer model, proposed byMills et al. in several publications [see, e.g., IEEE Trans. Plasma Sci. 31, 338 (2003)].

Spectroscopic measurement of electric field in dielectric barrier discharge in helium

Spatial distribution of electric field strength in dielectric barrier discharge in helium is determined from the Stark splitting and shifting of two visible helium lines and their forbidden components. Electric field is calculated by using spectral distance between forbidden and allowed components and results are compared to those obtained by using forbidden/allowed intensity ratio. Distributions of electric field, obtained for 200 and 800 mbar pressures, are typical for the glow mode of the discharge.

Doppler spectroscopy of hydrogen and deuterium Balmer alpha line in an abnormal glow discharge

The results of hydrogen and deuterium Balmer alpha line shapes and line intensities study in an abnormal glow discharge are reported and analyzed. The Doppler shifts along line wings are used to determine energies of excited hydrogen and deuterium atoms. For 12 different cathodes, intensity and shape of line wings are examined and dependence upon cathode material is determined. Tentative explanation of line wings intensity dependence is related to the sputtering of cathode material and back-scattering coefficients of incident hydrogen or deuterium ions and atoms from cathode surface. The influence of the light reflected on a cathode surface to the line shape measurements along discharge axis is considered. In hydrogen, deuterium, and Ar+3%H/sub 2/ discharges, basic mechanisms of fast hydrogen generation and excitation are studied. The shape and intensities of the H/sub /spl alpha// line profiles in pure hydrogen and in argon-hydrogen mixture may be correlated with hydrogen atom-carrier gas collision excitation cross sections. In order to assess the importance of reflected fast hydrogen atoms back scattered from the cathode surface, for the Balmer line shape formation, a simulation program is used. The results are in a qualitative agreement with Balmer line shapes observations.

Electric field measurement in the cathode fall region of a glow discharge in helium

Spatial distribution of electric field strength in the cathode fall region of an analytical glow discharge in helium and helium-hydrogen mixture is determined from the Stark splitting and shifting of three visible helium lines and their forbidden components. For this diagnostic technique the basic theory is outlined. The results in gas mixture agree well with electric fields determined from the shape of Hβ line.

Measurement of electric field development in dielectric barrier discharge in helium

In this paper the diffuse dielectric barrier discharge in helium was investigated using electrical measurements and time–space resolved optical emission spectroscopy. Electric field strength was measured using Stark polarization emission spectroscopy. Investigations were performed at 200 and 800 mbar pressures. It was found that the electric field strength was higher at the higher pressure while cathode fall length was shorter. During the whole discharge development period the length of the cathode fall region decreases. An interesting result is that in the period of current decrease, the maximum of the electric field distribution shifts away from the cathode showing the accumulation of negative charge near the cathode surface. (Some figures in this article are in colour only in the electronic version)